关于SQL语法
有如下SQL语句,请教几个问题。SELECT
CONVERT(VARCHAR(20),d.CZRQ) AS KEY1,
0 AS WDLY,
d.QYNM AS QYNM,
FROM ZS_MX d
WHERE
d.HZLXHRQ >= @BeginDate
UNION
SELECT
0 AS WDLY,
1 AS RTKBJ,
d.SSZZRQ,
CONVERT(VARCHAR(20),d.KPS) AS SE,
FROM ZS_MX d
WHERE
d.HZLXHRQ >= @BeginDate
1、select后面跟着的CONVERT(VARCHAR(20),d.CZRQ)的意思是什么?
2、AS KEY1什么意思?
3、UNION什么意思?
谢谢了!