Question

How do I convert all smallint type columns from my database to bit types?
I am using SQL Server 2008.

Answer 1

In SQL Server you can do it with ALTER TABLE my_table ALTER COLUMN my_column [new_datatype].

Be careful of things like default values because I haven’t tested with them.

Example 1 – will give a list of queries for you to review / amend / execute (safer option).

DECLARE @TableSchema VARCHAR(100)
DECLARE @TableName VARCHAR(100)
DECLARE @ColumnName VARCHAR(100)
DECLARE @Query NVARCHAR(1000)

DECLARE @FromDataType NVARCHAR(50)
DECLARE @ToDataType NVARCHAR(50)

SET @TableSchema = 'dbo';
SET @FromDataType = 'smallint';
SET @ToDataType = 'bit';

DECLARE c CURSOR FAST_FORWARD FOR 
    SELECT TABLE_NAME, COLUMN_NAME 
    FROM   INFORMATION_SCHEMA.COLUMNS 
    WHERE  TABLE_SCHEMA = @TableSchema 
       AND TABLE_NAME <> 'sysdiagrams' 
       AND DATA_TYPE = @FromDataType

OPEN c;

FETCH NEXT FROM c INTO @TableName, @ColumnName;

WHILE @@FETCH_STATUS = 0
BEGIN
    SET @Query = N'ALTER TABLE ' + @TableName + N' ALTER COLUMN ' + @ColumnName + N' ' + @ToDataType -- + CHAR(13) + N'GO'
    PRINT @Query

    EXEC sp_EXECUTESQL @Query

    FETCH NEXT FROM c INTO @TableName, @ColumnName;
END

CLOSE c;
DEALLOCATE c;

Example 2 – will execute (recommend running example 1 first!)

DECLARE @TableSchema VARCHAR(100)
DECLARE @TableName VARCHAR(100)
DECLARE @ColumnName VARCHAR(100)
DECLARE @Query NVARCHAR(1000)

DECLARE @FromDataType NVARCHAR(50)
DECLARE @ToDataType NVARCHAR(50)

SET @TableSchema = 'dbo';
SET @FromDataType = 'smallint';
SET @ToDataType = 'bit';

DECLARE c CURSOR FAST_FORWARD FOR 
    SELECT TABLE_NAME, COLUMN_NAME 
    FROM   INFORMATION_SCHEMA.COLUMNS 
    WHERE  TABLE_SCHEMA = @TableSchema 
       AND TABLE_NAME <> 'sysdiagrams' 
       AND DATA_TYPE = @FromDataType

OPEN c;

FETCH NEXT FROM c INTO @TableName, @ColumnName;

WHILE @@FETCH_STATUS = 0
BEGIN
    SET @Query = N'ALTER TABLE ' + @TableName + N' ALTER COLUMN ' + @ColumnName + N' ' + @ToDataType + CHAR(13) + N' GO'
    PRINT @Query

    FETCH NEXT FROM c INTO @TableName, @ColumnName;
END

CLOSE c;
DEALLOCATE c;