sql-server - 在 IF 部分内创建过程

Question

我需要一些有关简单 SQL 代码的帮助:

DECLARE @procExists int
SET @procExists = (SELECT COUNT(*) FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_SCHEMA = 'dbo' AND ROUTINE_NAME = 'Table_Exists' AND ROUTINE_TYPE = 'PROCEDURE')
IF NOT @procExists > 0 
BEGIN
    -- test query
    -- SELECT 'Something' = @procExists;

    -- error throwing code
    -- CREATE PROCEDURE Table_Exists
    --     @schemaName varchar(50),
    --     @tableName varchar(50)
    -- AS
    --     RETURN (SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = @schemaName AND TABLE_NAME = @tableName)
END

上面的简单代码:
- 声明一个 int 变量
- 检查过程 dbo.Table_Exists 是否存在
- 如果不存在则创建它

我的问题是这个错误信息:

Msg 156, Level 15, State 1, Line 9
Incorrect syntax near the keyword 'PROCEDURE'.
Msg 137, Level 15, State 2, Line 13
Must declare the scalar variable "@schemaName".

我不知道为什么，但是..
- 当我单独执行“CREATE PROCEDURE”主体时，它可以工作
- 当我执行整个 IF 部分排除'CREATE PROCEDURE'主体时，简单的查询有效
- 当我执行整个 IF 部分包括“CREATE PROCEDURE”主体时，会引发错误

我错过了什么？

Answer 1

CREATE PROCEDURE 必须在它自己的批处理中

所以，动态 SQL 是一种方法:

IF OBJECT_ID('Table_Exists') IS NULL
BEGIN
    EXEC ('CREATE PROCEDURE Table_Exists
         @schemaName varchar(50),
         @tableName varchar(50)
     AS
         RETURN (SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = @schemaName AND TABLE_NAME = @tableName)
')
END

或者先删除

IF OBJECT_ID('Table_Exists') IS NOT NULL
  DROP PROC Table_Exists
GO
CREATE PROCEDURE Table_Exists
         @schemaName varchar(50),
         @tableName varchar(50)
     AS
         RETURN (SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = @schemaName AND TABLE_NAME = @tableName)
GO

注意使用 OBJECT_ID 来查看过程是否存在。