Determining single-column candidate keys

This script will tell you all of the unique columns (except BLOBs) in
all of the tables in a database.
I made a post last night with some VBA code for exporting data from
Access. I've been given a 2 GB Access database with scores of tables,
some of them having hundreds of columns, millions of rows, and no
constraints. I also know very little about the underlying data. After
getting the data into SQL Server, I wanted to learn more about the
nature of the data. The first thing I wanted to find was which columns
could be single-column candidate keys.
One of the issues I ran into is that my generated SQL often exceeded
4000 characters, so I needed to come up with a way of executing more
than 4000 characters. Also, y'all'll notice that I'm using cursors
quite a bit here. These cursors only iterate through a few rows. The
heavy stuff is pretty efficient SQL.
-Alan
SET NOCOUNT ON
CREATE TABLE #UniqueColumns
(
TableName sysname
, ColumnName sysname
, IsUnique CHAR(1)
, PRIMARY KEY (TableName, ColumnName)
)
DECLARE @.TableName sysname
, @.ColumnName sysname
DECLARE cTables CURSOR
LOCAL
FAST_FORWARD
FOR
SELECT TABLE_NAME
FROM INFORMATION_SCHEMA.TABLES
CREATE TABLE #SQLFragments
(
RowNumber INT
IDENTITY
, SQL NVARCHAR(4000)
, Type VARCHAR(6)
NOT NULL
CHECK (Type IN ('SELECT', 'UPDATE'))
)
OPEN cTables
WHILE 1 = 1 BEGIN
FETCH NEXT FROM cTables INTO @.TableName
IF @.@.FETCH_STATUS <> 0 BREAK
DECLARE @.SQL NVARCHAR(4000)
, @.SQLUpdateUnique NVARCHAR(4000)
SET @.SQL = N'SELECT '
SET @.SQLUpdateUnique = N''
DECLARE c CURSOR
LOCAL
FAST_FORWARD
FOR
SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.columns
WHERE TABLE_NAME = @.TableName
AND DATA_TYPE NOT IN ('text', 'ntext', 'image')
ORDER BY ORDINAL_POSITION
OPEN c
WHILE 1 = 1 BEGIN
FETCH NEXT FROM c INTO @.ColumnName
IF @.@.FETCH_STATUS <> 0 BREAK
INSERT #UniqueColumns (TableName, ColumnName)
SELECT @.TableName, @.ColumnName
SET @.SQL = @.SQL + '
CASE WHEN COUNT (DISTINCT ' + @.ColumnName + ') = COUNT(*) THEN ''Y''
ELSE ''N'' END ' + @.ColumnName + ','
SET @.SQLUpdateUnique = @.SQLUpdateUnique + 'UPDATE #UniqueColumns SET
IsUnique = ' + @.ColumnName + ' FROM ##Temp WHERE TableName = ''' +
@.TableName + ''' AND ColumnName = ''' + @.ColumnName + '''
'
IF LEN(@.SQL) > 3000 BEGIN
INSERT #SQLFragments (SQL, Type)
SELECT @.SQL, 'SELECT'
SET @.SQL = ''
END
IF LEN(@.SQLUpdateUnique) > 3000 BEGIN
INSERT #SQLFragments (SQL, Type)
SELECT @.SQLUpdateUnique, 'UPDATE'
SET @.SQLUpdateUnique = ''
END
END
CLOSE c
DEALLOCATE c
SET @.SQL = LEFT(@.SQL, LEN(@.SQL) - 1) + ' INTO ##Temp FROM ' +
@.TableName
INSERT #SQLFragments (SQL, Type)
SELECT @.SQL, 'SELECT'
INSERT #SQLFragments (SQL, Type)
SELECT @.SQLUpdateUnique, 'UPDATE'
DECLARE @.FragmentCount INT
SELECT @.FragmentCount = COUNT(*) FROM #SQLFragments WHERE Type =
'SELECT'
DECLARE @.SQLEXEC NVARCHAR(4000)
, @.Fragment NVARCHAR(4000)
, @.RowNumber VARCHAR(10)
SET @.SQL = N''
SET @.SQLEXEC = N'EXEC ('
DECLARE cFragments CURSOR
LOCAL
FAST_FORWARD
FOR
SELECT SQL, RowNumber
FROM #SQLFragments
WHERE Type = 'SELECT'
ORDER BY RowNumber
OPEN cFragments
WHILE 1 = 1 BEGIN
FETCH NEXT FROM cFragments INTO @.Fragment, @.RowNumber
IF @.@.FETCH_STATUS <> 0 BREAK
SET @.SQL = @.SQL + N'DECLARE @.SQL' + @.RowNumber + N' NVARCHAR(4000)
SELECT @.SQL' + @.RowNumber + N' = SQL FROM #SQLFragments WHERE RowNumber
= ' + @.RowNumber + N'
'
SET @.SQLEXEC = @.SQLEXEC + N' @.SQL' + @.RowNumber + N' +'
END
CLOSE cFragments
DEALLOCATE cFragments
SET @.SQLEXEC = LEFT(@.SQLEXEC, LEN(@.SQLEXEC) - 1) + ')'
SET @.SQL = @.SQL + N' ' + @.SQLEXEC
EXEC sp_executesql @.SQL
SET @.SQL = N''
SET @.SQLEXEC = N'EXEC ('
DECLARE cFragments CURSOR
LOCAL
FAST_FORWARD
FOR
SELECT SQL, RowNumber
FROM #SQLFragments
WHERE Type = 'UPDATE'
ORDER BY RowNumber
OPEN cFragments
WHILE 1 = 1 BEGIN
FETCH NEXT FROM cFragments INTO @.Fragment, @.RowNumber
IF @.@.FETCH_STATUS <> 0 BREAK
SET @.SQL = @.SQL + N'DECLARE @.SQL' + @.RowNumber + N' NVARCHAR(4000)
SELECT @.SQL' + @.RowNumber + N' = SQL FROM #SQLFragments WHERE RowNumber
= ' + @.RowNumber + N'
'
SET @.SQLEXEC = @.SQLEXEC + N' @.SQL' + @.RowNumber + N' +'
END
CLOSE cFragments
DEALLOCATE cFragments
SET @.SQL = @.SQL + N' ' + LEFT(@.SQLEXEC, LEN(@.SQLEXEC) - 1) + N')'
EXEC sp_executesql @.SQL
DELETE #SQLFragments
DROP TABLE ##Temp
END
CLOSE cTables
DEALLOCATE cTables
DELETE #UniqueColumns WHERE IsUnique = 'N'
SELECT * FROM #UniqueColumns
DROP TABLE #UniqueColumns
DROP TABLE #SQLFragmentsYou can analyze the data and make assumptions about keys and relationships,
but can the source of the data also provide a data dictionary?
"Alan Samet" <alansamet@.gmail.com> wrote in message
news:1141922084.124478.54740@.j52g2000cwj.googlegroups.com...
> This script will tell you all of the unique columns (except BLOBs) in
> all of the tables in a database.
> I made a post last night with some VBA code for exporting data from
> Access. I've been given a 2 GB Access database with scores of tables,
> some of them having hundreds of columns, millions of rows, and no
> constraints. I also know very little about the underlying data. After
> getting the data into SQL Server, I wanted to learn more about the
> nature of the data. The first thing I wanted to find was which columns
> could be single-column candidate keys.
> One of the issues I ran into is that my generated SQL often exceeded
> 4000 characters, so I needed to come up with a way of executing more
> than 4000 characters. Also, y'all'll notice that I'm using cursors
> quite a bit here. These cursors only iterate through a few rows. The
> heavy stuff is pretty efficient SQL.
> -Alan
> SET NOCOUNT ON
> CREATE TABLE #UniqueColumns
> (
> TableName sysname
> , ColumnName sysname
> , IsUnique CHAR(1)
> , PRIMARY KEY (TableName, ColumnName)
> )
> DECLARE @.TableName sysname
> , @.ColumnName sysname
> DECLARE cTables CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT TABLE_NAME
> FROM INFORMATION_SCHEMA.TABLES
> CREATE TABLE #SQLFragments
> (
> RowNumber INT
> IDENTITY
> , SQL NVARCHAR(4000)
> , Type VARCHAR(6)
> NOT NULL
> CHECK (Type IN ('SELECT', 'UPDATE'))
> )
> OPEN cTables
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM cTables INTO @.TableName
> IF @.@.FETCH_STATUS <> 0 BREAK
> DECLARE @.SQL NVARCHAR(4000)
> , @.SQLUpdateUnique NVARCHAR(4000)
> SET @.SQL = N'SELECT '
> SET @.SQLUpdateUnique = N''
> DECLARE c CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT COLUMN_NAME
> FROM INFORMATION_SCHEMA.columns
> WHERE TABLE_NAME = @.TableName
> AND DATA_TYPE NOT IN ('text', 'ntext', 'image')
> ORDER BY ORDINAL_POSITION
> OPEN c
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM c INTO @.ColumnName
> IF @.@.FETCH_STATUS <> 0 BREAK
> INSERT #UniqueColumns (TableName, ColumnName)
> SELECT @.TableName, @.ColumnName
> SET @.SQL = @.SQL + '
> CASE WHEN COUNT (DISTINCT ' + @.ColumnName + ') = COUNT(*) THEN ''Y''
> ELSE ''N'' END ' + @.ColumnName + ','
> SET @.SQLUpdateUnique = @.SQLUpdateUnique + 'UPDATE #UniqueColumns SET
> IsUnique = ' + @.ColumnName + ' FROM ##Temp WHERE TableName = ''' +
> @.TableName + ''' AND ColumnName = ''' + @.ColumnName + '''
> '
> IF LEN(@.SQL) > 3000 BEGIN
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQL, 'SELECT'
> SET @.SQL = ''
> END
> IF LEN(@.SQLUpdateUnique) > 3000 BEGIN
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQLUpdateUnique, 'UPDATE'
> SET @.SQLUpdateUnique = ''
> END
> END
> CLOSE c
> DEALLOCATE c
> SET @.SQL = LEFT(@.SQL, LEN(@.SQL) - 1) + ' INTO ##Temp FROM ' +
> @.TableName
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQL, 'SELECT'
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQLUpdateUnique, 'UPDATE'
> DECLARE @.FragmentCount INT
> SELECT @.FragmentCount = COUNT(*) FROM #SQLFragments WHERE Type =
> 'SELECT'
> DECLARE @.SQLEXEC NVARCHAR(4000)
> , @.Fragment NVARCHAR(4000)
> , @.RowNumber VARCHAR(10)
> SET @.SQL = N''
> SET @.SQLEXEC = N'EXEC ('
> DECLARE cFragments CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT SQL, RowNumber
> FROM #SQLFragments
> WHERE Type = 'SELECT'
> ORDER BY RowNumber
> OPEN cFragments
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM cFragments INTO @.Fragment, @.RowNumber
> IF @.@.FETCH_STATUS <> 0 BREAK
> SET @.SQL = @.SQL + N'DECLARE @.SQL' + @.RowNumber + N' NVARCHAR(4000)
> SELECT @.SQL' + @.RowNumber + N' = SQL FROM #SQLFragments WHERE RowNumber
> = ' + @.RowNumber + N'
> '
> SET @.SQLEXEC = @.SQLEXEC + N' @.SQL' + @.RowNumber + N' +'
> END
> CLOSE cFragments
> DEALLOCATE cFragments
> SET @.SQLEXEC = LEFT(@.SQLEXEC, LEN(@.SQLEXEC) - 1) + ')'
> SET @.SQL = @.SQL + N' ' + @.SQLEXEC
> EXEC sp_executesql @.SQL
> SET @.SQL = N''
> SET @.SQLEXEC = N'EXEC ('
> DECLARE cFragments CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT SQL, RowNumber
> FROM #SQLFragments
> WHERE Type = 'UPDATE'
> ORDER BY RowNumber
> OPEN cFragments
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM cFragments INTO @.Fragment, @.RowNumber
> IF @.@.FETCH_STATUS <> 0 BREAK
> SET @.SQL = @.SQL + N'DECLARE @.SQL' + @.RowNumber + N' NVARCHAR(4000)
> SELECT @.SQL' + @.RowNumber + N' = SQL FROM #SQLFragments WHERE RowNumber
> = ' + @.RowNumber + N'
> '
> SET @.SQLEXEC = @.SQLEXEC + N' @.SQL' + @.RowNumber + N' +'
> END
> CLOSE cFragments
> DEALLOCATE cFragments
> SET @.SQL = @.SQL + N' ' + LEFT(@.SQLEXEC, LEN(@.SQLEXEC) - 1) + N')'
> EXEC sp_executesql @.SQL
> DELETE #SQLFragments
> DROP TABLE ##Temp
> END
> CLOSE cTables
> DEALLOCATE cTables
> DELETE #UniqueColumns WHERE IsUnique = 'N'
> SELECT * FROM #UniqueColumns
> DROP TABLE #UniqueColumns
> DROP TABLE #SQLFragments
>|||I can't get a data dictionary. This data is only in intermediate form
anyways. I'm writing my own database for the front-end application, but
I need some of the data that's in this database. A lot of it's not
normalized, et cetera. Once I know exactly what I need for my
application, the database I write will be properly constrained. The
purpose of the script was to reduce the amount of time it takes me to
understand the underlying data.
-Alan|||Alan,
I believe it's possible to execute longer strings by combining them and
using EXEC instead of sp_executesql eg:
EXEC( @.select + ' ' + @.from )
However, that should probably telling you there might be another way to do
it. How about capturing your information first?
ie have two tables, one to represent the tables in your Access database and
one to represent the columns ( or attributes Joe )? Something like:
Table: access_tables
at_id
table_name
rows
Table: access_fields
af_id
at_id
field_name
unique values
rows
Run one script which captures the data required, then you can run nice fast
SELECTs on real data:
SELECT *
FROM access_tables t
INNER JOIN access_fields f ON t.at_id = f.at_id
WHERE t.rows = f.unique_values
It's sometimes frowned upon to gather metadata like this in your database
but I see what you're trying to do.
Have fun!
Damien
"Alan Samet" wrote:

> This script will tell you all of the unique columns (except BLOBs) in
> all of the tables in a database.
> I made a post last night with some VBA code for exporting data from
> Access. I've been given a 2 GB Access database with scores of tables,
> some of them having hundreds of columns, millions of rows, and no
> constraints. I also know very little about the underlying data. After
> getting the data into SQL Server, I wanted to learn more about the
> nature of the data. The first thing I wanted to find was which columns
> could be single-column candidate keys.
> One of the issues I ran into is that my generated SQL often exceeded
> 4000 characters, so I needed to come up with a way of executing more
> than 4000 characters. Also, y'all'll notice that I'm using cursors
> quite a bit here. These cursors only iterate through a few rows. The
> heavy stuff is pretty efficient SQL.
> -Alan
> SET NOCOUNT ON
> CREATE TABLE #UniqueColumns
> (
> TableName sysname
> , ColumnName sysname
> , IsUnique CHAR(1)
> , PRIMARY KEY (TableName, ColumnName)
> )
> DECLARE @.TableName sysname
> , @.ColumnName sysname
> DECLARE cTables CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT TABLE_NAME
> FROM INFORMATION_SCHEMA.TABLES
> CREATE TABLE #SQLFragments
> (
> RowNumber INT
> IDENTITY
> , SQL NVARCHAR(4000)
> , Type VARCHAR(6)
> NOT NULL
> CHECK (Type IN ('SELECT', 'UPDATE'))
> )
> OPEN cTables
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM cTables INTO @.TableName
> IF @.@.FETCH_STATUS <> 0 BREAK
> DECLARE @.SQL NVARCHAR(4000)
> , @.SQLUpdateUnique NVARCHAR(4000)
> SET @.SQL = N'SELECT '
> SET @.SQLUpdateUnique = N''
> DECLARE c CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT COLUMN_NAME
> FROM INFORMATION_SCHEMA.columns
> WHERE TABLE_NAME = @.TableName
> AND DATA_TYPE NOT IN ('text', 'ntext', 'image')
> ORDER BY ORDINAL_POSITION
> OPEN c
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM c INTO @.ColumnName
> IF @.@.FETCH_STATUS <> 0 BREAK
> INSERT #UniqueColumns (TableName, ColumnName)
> SELECT @.TableName, @.ColumnName
> SET @.SQL = @.SQL + '
> CASE WHEN COUNT (DISTINCT ' + @.ColumnName + ') = COUNT(*) THEN ''Y''
> ELSE ''N'' END ' + @.ColumnName + ','
> SET @.SQLUpdateUnique = @.SQLUpdateUnique + 'UPDATE #UniqueColumns SET
> IsUnique = ' + @.ColumnName + ' FROM ##Temp WHERE TableName = ''' +
> @.TableName + ''' AND ColumnName = ''' + @.ColumnName + '''
> '
> IF LEN(@.SQL) > 3000 BEGIN
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQL, 'SELECT'
> SET @.SQL = ''
> END
> IF LEN(@.SQLUpdateUnique) > 3000 BEGIN
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQLUpdateUnique, 'UPDATE'
> SET @.SQLUpdateUnique = ''
> END
> END
> CLOSE c
> DEALLOCATE c
> SET @.SQL = LEFT(@.SQL, LEN(@.SQL) - 1) + ' INTO ##Temp FROM ' +
> @.TableName
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQL, 'SELECT'
> INSERT #SQLFragments (SQL, Type)
> SELECT @.SQLUpdateUnique, 'UPDATE'
> DECLARE @.FragmentCount INT
> SELECT @.FragmentCount = COUNT(*) FROM #SQLFragments WHERE Type =
> 'SELECT'
> DECLARE @.SQLEXEC NVARCHAR(4000)
> , @.Fragment NVARCHAR(4000)
> , @.RowNumber VARCHAR(10)
> SET @.SQL = N''
> SET @.SQLEXEC = N'EXEC ('
> DECLARE cFragments CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT SQL, RowNumber
> FROM #SQLFragments
> WHERE Type = 'SELECT'
> ORDER BY RowNumber
> OPEN cFragments
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM cFragments INTO @.Fragment, @.RowNumber
> IF @.@.FETCH_STATUS <> 0 BREAK
> SET @.SQL = @.SQL + N'DECLARE @.SQL' + @.RowNumber + N' NVARCHAR(4000)
> SELECT @.SQL' + @.RowNumber + N' = SQL FROM #SQLFragments WHERE RowNumber
> = ' + @.RowNumber + N'
> '
> SET @.SQLEXEC = @.SQLEXEC + N' @.SQL' + @.RowNumber + N' +'
> END
> CLOSE cFragments
> DEALLOCATE cFragments
> SET @.SQLEXEC = LEFT(@.SQLEXEC, LEN(@.SQLEXEC) - 1) + ')'
> SET @.SQL = @.SQL + N' ' + @.SQLEXEC
> EXEC sp_executesql @.SQL
> SET @.SQL = N''
> SET @.SQLEXEC = N'EXEC ('
> DECLARE cFragments CURSOR
> LOCAL
> FAST_FORWARD
> FOR
> SELECT SQL, RowNumber
> FROM #SQLFragments
> WHERE Type = 'UPDATE'
> ORDER BY RowNumber
> OPEN cFragments
> WHILE 1 = 1 BEGIN
> FETCH NEXT FROM cFragments INTO @.Fragment, @.RowNumber
> IF @.@.FETCH_STATUS <> 0 BREAK
> SET @.SQL = @.SQL + N'DECLARE @.SQL' + @.RowNumber + N' NVARCHAR(4000)
> SELECT @.SQL' + @.RowNumber + N' = SQL FROM #SQLFragments WHERE RowNumber
> = ' + @.RowNumber + N'
> '
> SET @.SQLEXEC = @.SQLEXEC + N' @.SQL' + @.RowNumber + N' +'
> END
> CLOSE cFragments
> DEALLOCATE cFragments
> SET @.SQL = @.SQL + N' ' + LEFT(@.SQLEXEC, LEN(@.SQLEXEC) - 1) + N')'
> EXEC sp_executesql @.SQL
> DELETE #SQLFragments
> DROP TABLE ##Temp
> END
> CLOSE cTables
> DEALLOCATE cTables
> DELETE #UniqueColumns WHERE IsUnique = 'N'
> SELECT * FROM #UniqueColumns
> DROP TABLE #UniqueColumns
> DROP TABLE #SQLFragments
>|||>> .. and one to represent the columns ( or attributes Joe )? <<
LOL! Eitgher, but not "fields", please !
We can avoid the metadata with a little work. Pull out the table and
column names then use a text editor to generate queries with this
template
/*
DROP TABLE Foobar;
CREATE TABLE Foobar
(known_key CHAR(2) NOT NULL PRIMARY KEY,
actual_key CHAR(2) NOT NULL,
non_key CHAR(2) NOT NULL,
non_key_null CHAR(2));
INSERT INTO Foobar VALUES ('K1', 'a', 'x', 'a');
INSERT INTO Foobar VALUES ('K2', 'b', 'x', NULL);
INSERT INTO Foobar VALUES ('K3', 'c', 'x', 'b');
INSERT INTO Foobar VALUES ('K4', 'd', 'y', 'c');
INSERT INTO Foobar VALUES ('K5', 'e', 'y', 'd');
INSERT INTO Foobar VALUES ('K6', 'f', 'y', 'e');
*/
SELECT 'Foobar' AS table_name,
CASE WHEN COUNT(DISTINCT known_key) = COUNT(*)
THEN 'Y' ELSE 'N' END AS known_key,
CASE WHEN COUNT(DISTINCT actual_key) = COUNT(*)
THEN 'Y' ELSE 'N' END AS actual_key,
CASE WHEN COUNT(DISTINCT non_key) = COUNT(*)
THEN 'Y' ELSE 'N' END AS non_key,
CASE WHEN COUNT(DISTINCT non_key_null) = COUNT(*)
THEN 'Y' ELSE 'N' END AS non_key_null
FROM Foobar
These should run faster than a cursor. NULLs and dups will cause
COUNT(*) and COUNT(DISTINCT col) to be unequal. COUNT(*) should be
computed only once, and the optimizer should catch NOT NULL UNIQUE
constraints to short-cut the equality test.
No need for loops.|||Joe, that's almost exactly what I did. The cursors were used for two
things:
building dynamic SQL statements for the select case when count(...)
statements and the update statement to update my result table. I
prioritized execution efficiency of the queries that determined
uniqueness over query generation.
In more detail, the technique I used is as follows.
Here is your table w/ unknown constraints:
CREATE TABLE Foobar
(
Column0 DATATYPE
, Column1 DATATYPE
..
, Column 499 DATATYPE
)
First, I created a table of all table names and column names with a
column to indicate whether the value was unique.
CREATE TABLE #UniqueColumns
(
TableName sysname
, ColumnName sysname
, IsUnique CHAR(1)
, PRIMARY KEY (TableName, ColumnName)
)
Next, for each table I determined which columns were unique. Since I'm
dealing with lots of records, I wanted this to be the most efficient.
I'd say this query did the trick.
SELECT CASE WHEN COUNT(DISTINCT Column0) = COUNT(*) THEN 'Y' ELSE 'N'
END Column0
, CASE WHEN COUNT(DISTINCT Column1) = COUNT(*) THEN 'Y' ELSE 'N' END
Column1
, CASE WHEN COUNT(DISTINCT Column2) = COUNT(*) THEN 'Y' ELSE 'N' END
Column2
... et cetera
INTO ##Temp
FROM TableName
I then updated my table with table and column names:
UPDATE #UniqueColumns SET IsUnique = Column0 FROM ##Temp WHERE
TableName = 'TableName' AND ColumnName = 'Column0'
UPDATE #UniqueColumns SET IsUnique = Column1 FROM ##Temp WHERE
TableName = 'TableName' AND ColumnName = 'Column1'
The only issue here was when my SQL exceeded 4000 characters. So, I
went ahead and created a temporary table to store the fragments. This
is one of the few cases where the IDENTITY keyword is actually useful.
The latter part of the query would take and create a script that looked
like the following and execute it:
DECLARE @.SQL1 NVARCHAR(4000)
SELECT @.SQL1 = SQL FROM #SQLFragments WHERE RowNumber = 1
DECLARE @.SQL2 NVARCHAR(4000)
SELECT @.SQL2 = SQL FROM #SQLFragments WHERE RowNumber = 2
EXEC (@.SQL1 + @.SQL2)
et cetera. This was my dynamic workaround for the 4000 character
limitation. In reality, I doubt anything would gone over 12,000, so I
could've probably gotten away with just a couple variables, but this
was way more fun.
-Alan
--CELKO-- wrote:
> LOL! Eitgher, but not "fields", please !
>
> We can avoid the metadata with a little work. Pull out the table and
> column names then use a text editor to generate queries with this
> template
> /*
> DROP TABLE Foobar;
> CREATE TABLE Foobar
> (known_key CHAR(2) NOT NULL PRIMARY KEY,
> actual_key CHAR(2) NOT NULL,
> non_key CHAR(2) NOT NULL,
> non_key_null CHAR(2));
> INSERT INTO Foobar VALUES ('K1', 'a', 'x', 'a');
> INSERT INTO Foobar VALUES ('K2', 'b', 'x', NULL);
> INSERT INTO Foobar VALUES ('K3', 'c', 'x', 'b');
> INSERT INTO Foobar VALUES ('K4', 'd', 'y', 'c');
> INSERT INTO Foobar VALUES ('K5', 'e', 'y', 'd');
> INSERT INTO Foobar VALUES ('K6', 'f', 'y', 'e');
> */
> SELECT 'Foobar' AS table_name,
> CASE WHEN COUNT(DISTINCT known_key) = COUNT(*)
> THEN 'Y' ELSE 'N' END AS known_key,
> CASE WHEN COUNT(DISTINCT actual_key) = COUNT(*)
> THEN 'Y' ELSE 'N' END AS actual_key,
> CASE WHEN COUNT(DISTINCT non_key) = COUNT(*)
> THEN 'Y' ELSE 'N' END AS non_key,
> CASE WHEN COUNT(DISTINCT non_key_null) = COUNT(*)
> THEN 'Y' ELSE 'N' END AS non_key_null
> FROM Foobar
> These should run faster than a cursor. NULLs and dups will cause
> COUNT(*) and COUNT(DISTINCT col) to be unequal. COUNT(*) should be
> computed only once, and the optimizer should catch NOT NULL UNIQUE
> constraints to short-cut the equality test.
> No need for loops.|||Alan,
Neat stuff!
My simpleminded approach to the same sort of problem follows. It
doesn't use the owner or schema, as it should, and doesn't filter on
datatypes, as it should, but the general idea is clear enough I think.
The first column of the result tells you the table name and the number
of rows, and I scan visually for the candidate keys. On the other
hand, it gives me a complete picture of how many values per column,
and that can be invaluable to sorting out mysterious data.
Roy Harvey
Beacon Falls, CT
SELECT CASE WHEN ORDINAL_POSITION = 1
THEN 'SELECT COUNT(*) as ' + TABLE_NAME + ',' +
char(13) + char(10)
ELSE ''
END +
' COUNT(distinct ' + COLUMN_NAME + ') as ' + COLUMN_NAME
+
CASE WHEN ORDINAL_POSITION <
(select max(ORDINAL_POSITION)
from INFORMATION_SCHEMA.COLUMNS as L
where C.TABLE_NAME = L.TABLE_NAME)
THEN ','
ELSE char(13) + char(10) +
' FROM ' + TABLE_NAME
END
from INFORMATION_SCHEMA.COLUMNS as C
order by TABLE_NAME, ORDINAL_POSITION