WHERE EXISTS子句中的SQL Server语法问题

Question

我遇到问题，让以下查询在UPDATE命令下正常运行，但在我只是尝试对数据执行等效SELECT时却没有。我在WHERE EXISTS段上收到“语法错误”。我尝试修改WHERE EXISTS以包含它之前的AND，但后来又出现了另一种语法错误：

  

在期望条件的上下文中指定的非布尔类型的表达式

原始SQL UPDATE声明：

UPDATE PS_RPLN_MSTR_TAO5 
SET QTY_WIP_BASE = (SELECT A.QTY 
                    FROM PS_WIP_QTY_INV_VW A 
                    WHERE A.BUSINESS_UNIT = PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN 
                      AND A.INV_ITEM_ID = PS_RPLN_MSTR_TAO5.INV_ITEM_ID 
                      AND PS_RPLN_MSTR_TAO5.INCL_WIP_QTY_FLG = 'Y' 
                      AND PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN = '82DDR' 
                      AND PS_RPLN_MSTR_TAO5.PROCESS_INSTANCE = '8193747')    
 WHERE EXISTS (SELECT 'X' 
               FROM PS_WIP_QTY_INV_VW A 
               WHERE A.BUSINESS_UNIT = PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN 
                 AND A.INV_ITEM_ID = PS_RPLN_MSTR_TAO5.INV_ITEM_ID 
                 AND PS_RPLN_MSTR_TAO5.INCL_WIP_QTY_FLG = 'Y' 
                 AND PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN = '82DDR' 
                 AND PS_RPLN_MSTR_TAO5.PROCESS_INSTANCE = '8193747')

修改SELECT查询（获取语法错误）：

SELECT 
    A.QTY 
FROM
    PS_WIP_QTY_INV_VW A, PS_RPLN_MSTR_TAO5 
WHERE 
    A.BUSINESS_UNIT = PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN 
    AND A.INV_ITEM_ID = PS_RPLN_MSTR_TAO5.INV_ITEM_ID 
    AND PS_RPLN_MSTR_TAO5.INCL_WIP_QTY_FLG = 'Y' 
    AND PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN = '82DDR' 
    AND PS_RPLN_MSTR_TAO5.PROCESS_INSTANCE = '8193747' 
WHERE 
    EXISTS (SELECT 'X' 
            FROM PS_WIP_QTY_INV_VW A, PS_RPLN_MSTR_TAO5 
            WHERE A.BUSINESS_UNIT = PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN 
              AND A.INV_ITEM_ID = PS_RPLN_MSTR_TAO5.INV_ITEM_ID 
              AND PS_RPLN_MSTR_TAO5.INCL_WIP_QTY_FLG = 'Y' 
              AND PS_RPLN_MSTR_TAO5.BUSINESS_UNIT_IN = '82DDR' 
              AND PS_RPLN_MSTR_TAO5.PROCESS_INSTANCE = '8193747')