为 SQL 中的所有可为空的列设置 NULL

Question

我遇到以下问题：早期版本的数据库使用值“”而不是 NULL。如果列可以为空，我现在必须将这些值在它们存在的任何地方转换为 NULL。

我试过以下代码：

BEGIN TRAN
DECLARE 
    @curcolumn VARCHAR(MAX),
    @curtable VARCHAR(MAX);

DECLARE cursor_setnull CURSOR
FOR SELECT INFORMATION_SCHEMA.TABLES.TABLE_NAME, INFORMATION_SCHEMA.COLUMNS.COLUMN_NAME FROM INFORMATION_SCHEMA.TABLES
JOIN INFORMATION_SCHEMA.COLUMNS ON INFORMATION_SCHEMA.TABLES.TABLE_NAME = INFORMATION_SCHEMA.COLUMNS.TABLE_NAME
WHERE INFORMATION_SCHEMA.COLUMNS.IS_NULLABLE = 'YES'

OPEN cursor_setnull

FETCH NEXT FROM cursor_setnull INTO
    @curcolumn,
    @curtable;

WHILE @@FETCH_STATUS = 0
    BEGIN
        FETCH NEXT FROM cursor_setnull INTO
            @curcolumn,
            @curtable;
        DECLARE @numrows INT;
        DECLARE @query NVARCHAR(MAX);
        set @query = 'UPDATE '+@curtable+' SET '+@curcolumn+' = NULL WHERE '+@curcolumn+' = '''''
        EXEC sp_executesql @query
    END;

CLOSE cursor_setnull;
DEALLOCATE cursor_setnull;
ROLLBACK

在运行，它为每一列提供以下错误：“无效的对象名称 'column_name'。

如果有人能帮我找出错误，我将不胜感激。

Answer 1

如果您查看生成的查询，您会发现查询不正确。

您需要更改将值提取到游标中的顺序。

FETCH NEXT FROM cursor_setnull INTO
    @curcolumn,
    @curtable;

应该是

FETCH NEXT FROM cursor_setnull INTO
    @curtable,    
    @curcolumn;

Answer 2

而不是使用 CURSOR，我会使用一些显式事务批量处理所有事务。我假设 SQL Server 2017+，由于当我问你使用的是什么版本时缺少回复：

DECLARE @SQL nvarchar(MAX),
        @CRLF nchar(2) = NCHAR(13) + NCHAR(10);

DECLARE @Delimiter nvarchar(10) = N',' + @CRLF + N'    ' 

SET @SQL = STUFF((SELECT @CRLF + N'BEGIN TRANSACTION;' + @CRLF +
                         N'    UPDATE ' + QUOTENAME(s.[name]) + N'.' + QUOTENAME(t.[name]) + @CRLF + 
                         N'    SET ' + (SELECT STRING_AGG(QUOTENAME(c.[name]) + N' = CASE ' + QUOTENAME(c.[name]) + N' WHEN '''' THEN NULL ELSE '+ QUOTENAME(c.[name]) + N' END',@Delimiter) WITHIN GROUP (ORDER BY c.column_id)
                                        FROM sys.columns c
                                             JOIN sys.types ct ON c.system_type_id = ct.system_type_id
                                        WHERE c.object_id = t.object_id
                                          AND ct.[name] IN ('varchar','nvarchar','char','nchar')
                                          AND c.is_nullable = 1
                                          AND c.is_computed = 0) + N';' + @CRLF + 
                        N'COMMIT TRANSACTION'
                  FROM sys.schemas s
                       JOIN sys.tables t ON s.schema_id = t.SCHEMA_ID
                  WHERE EXISTS (SELECT 1
                                FROM sys.columns c
                                     JOIN sys.types ct ON c.system_type_id = ct.system_type_id
                                WHERE c.object_id = t.object_id
                                AND ct.[name] IN ('varchar','nvarchar','char','nchar')
                                AND c.is_nullable = 1
                                AND c.is_computed = 0)
                  ORDER BY s.schema_id, t.object_id
                  FOR XML PATH(N''),TYPE).value('(./text())[1]','nvarchar(MAX)'),1,2,N'');

PRINT @SQL; --Your best friend

--EXEC sys.sp_executesql @SQL; --Uncomment to run dynamic statement.

为 SQL 中的所有可为空的列设置 NULL

Setting NULL for all nullable columns in SQL

sql-server

loops

database-cursor