Question

这是我的代码：

select a.id_brg, a.nm_brg, a.jen_sat, a.nm_kat,a.stok,a.laku, (a.stok-a.laku) as difference from (SELECT barang.id_brg, barang.nm_brg, jen_sat, nm_kat, SUM( IFNULL(  stok_brg.stok, 0 ) ) AS stok, IFNULL( laku, 0 ) AS laku
        FROM barang
        JOIN satuan ON barang.id_sat = satuan.id_sat
        JOIN kategori ON barang.id_kat = kategori.id_kat
        LEFT JOIN stok_brg ON barang.id_brg = stok_brg.id_brg
        LEFT JOIN (
        SELECT barang.id_brg, SUM( IFNULL( brg_laku.dibeli, 0 ) ) AS laku
        FROM barang, brg_laku
        WHERE barang.id_brg = brg_laku.id_brg
        GROUP BY barang.id_brg ASC
        ) AS brg_laku ON barang.id_brg = brg_laku.id_brg
        GROUP BY barang.id_brg ASC) as a;

如何在该代码中添加where？

where difference <= 3

每次写where时，都会收到错误消息：

未知列＆＃39;差异＆＃39;在where子句

Answer 1

尝试以下：

Select * from (select a.id_brg, a.nm_brg, a.jen_sat, a.nm_kat,a.stok,a.laku, (a.stok-a.laku) as difference from (SELECT barang.id_brg, barang.nm_brg, jen_sat, nm_kat, SUM( IFNULL(  stok_brg.stok, 0 ) ) AS stok, IFNULL( laku, 0 ) AS laku
        FROM barang
        JOIN satuan ON barang.id_sat = satuan.id_sat
        JOIN kategori ON barang.id_kat = kategori.id_kat
        LEFT JOIN stok_brg ON barang.id_brg = stok_brg.id_brg
        LEFT JOIN (
        SELECT barang.id_brg, SUM( IFNULL( brg_laku.dibeli, 0 ) ) AS laku
        FROM barang, brg_laku
        WHERE barang.id_brg = brg_laku.id_brg
        GROUP BY barang.id_brg ASC
        ) AS brg_laku ON barang.id_brg = brg_laku.id_brg
        GROUP BY barang.id_brg ASC) as a;select a.id_brg, a.nm_brg, a.jen_sat, a.nm_kat,a.stok,a.laku, (a.stok-a.laku) as difference from (SELECT barang.id_brg, barang.nm_brg, jen_sat, nm_kat, SUM( IFNULL(  stok_brg.stok, 0 ) ) AS stok, IFNULL( laku, 0 ) AS laku
        FROM barang
        JOIN satuan ON barang.id_sat = satuan.id_sat
        JOIN kategori ON barang.id_kat = kategori.id_kat
        LEFT JOIN stok_brg ON barang.id_brg = stok_brg.id_brg
        LEFT JOIN (
        SELECT barang.id_brg, SUM( IFNULL( brg_laku.dibeli, 0 ) ) AS laku
        FROM barang, brg_laku
        WHERE barang.id_brg = brg_laku.id_brg
        GROUP BY barang.id_brg ASC
        ) AS brg_laku ON barang.id_brg = brg_laku.id_brg
        GROUP BY barang.id_brg ASC) as a)fq where  difference <= 3

Answer 2

SELECT a.id_brg, 
       a.nm_brg, 
       a.jen_sat,
       a.nm_kat,
       a.stok,
       a.laku,
      (a.stok-a.laku) as difference 
FROM (
      SELECT barang.id_brg,
             barang.nm_brg,
             jen_sat, 
             nm_kat, 
             SUM(IFNULL(stok_brg.stok, 0)) AS stok,
             IFNULL(laku, 0) AS laku
      FROM barang
      JOIN satuan ON barang.id_sat = satuan.id_sat
      JOIN kategori ON barang.id_kat = kategori.id_kat
      LEFT JOIN stok_brg ON barang.id_brg = stok_brg.id_brg
      LEFT JOIN (
                 SELECT barang.id_brg,
                        SUM(IFNULL( brg_laku.dibeli, 0 )) AS laku
                 FROM barang 
                 INNER JOIN brg_laku
                 ON barang.id_brg = brg_laku.id_brg
                 GROUP BY barang.id_brg ASC
                ) AS brg_laku 
     ON barang.id_brg = brg_laku.id_brg
     GROUP BY barang.id_brg ASC
    ) as a
WHERE (a.stok-a.laku) <= 3;

现在，你能在MySQL的WHERE子句中使用别名吗？

来自MySQL手册：

不允许在WHERE子句中引用列别名因为WHERE时可能尚未确定列值子句被执行。见B.1.5.4，“Problems with Column Aliases”。

Answer 3

您无法在声明它的同一SELECT内引用列别名。您可以按列表达式（a.stok-a.laku）进行过滤，也可以将其嵌套为子查询，并在最外层范围内对其进行过滤。

按列表达式过滤：

select 
    a.id_brg, 
    a.nm_brg, 
    a.jen_sat, 
    a.nm_kat,
    a.stok,
    a.laku, 
    (a.stok-a.laku) as difference 
from 
    (SELECT 
        barang.id_brg, 
        barang.nm_brg, 
        jen_sat, 
        nm_kat, 
        SUM( IFNULL(  stok_brg.stok, 0 ) ) AS stok, IFNULL( laku, 0 ) AS laku
    FROM barang
        JOIN satuan ON barang.id_sat = satuan.id_sat
        JOIN kategori ON barang.id_kat = kategori.id_kat
        LEFT JOIN stok_brg ON barang.id_brg = stok_brg.id_brg
        LEFT JOIN (
            SELECT 
                barang.id_brg, 
                SUM( IFNULL( brg_laku.dibeli, 0 ) ) AS laku
            FROM 
                barang, brg_laku
            WHERE 
                barang.id_brg = brg_laku.id_brg
            GROUP BY 
                barang.id_brg ASC
            ) AS brg_laku 
                ON barang.id_brg = brg_laku.id_brg
    GROUP BY 
        barang.id_brg ASC) as a
WHERE
    a.stok-a.laku <= 3 -- Here!

嵌套子查询：

SELECT
    X.*
FROM
    (
    select 
        a.id_brg, 
        a.nm_brg, 
        a.jen_sat, 
        a.nm_kat,
        a.stok,
        a.laku, 
        (a.stok-a.laku) as difference 
    from 
        (SELECT 
            barang.id_brg, 
            barang.nm_brg, 
            jen_sat, 
            nm_kat, 
            SUM( IFNULL(  stok_brg.stok, 0 ) ) AS stok, IFNULL( laku, 0 ) AS laku
        FROM barang
            JOIN satuan ON barang.id_sat = satuan.id_sat
            JOIN kategori ON barang.id_kat = kategori.id_kat
            LEFT JOIN stok_brg ON barang.id_brg = stok_brg.id_brg
            LEFT JOIN (
                SELECT 
                    barang.id_brg, 
                    SUM( IFNULL( brg_laku.dibeli, 0 ) ) AS laku
                FROM 
                    barang, brg_laku
                WHERE 
                    barang.id_brg = brg_laku.id_brg
                GROUP BY 
                    barang.id_brg ASC
                ) AS brg_laku 
                    ON barang.id_brg = brg_laku.id_brg
        GROUP BY 
            barang.id_brg ASC) as a
    ) AS X
WHERE
    X.difference <= 3 -- Here!

Answer 4

使用WHERE (a.stok-a.laku) <= 3而不是别名。

SELECT a.id_brg, a.nm_brg, a.jen_sat, a.nm_kat,a.stok,a.laku, (a.stok-a.laku) difference FROM(SELECT B.id_brg, B.nm_brg, jen_sat, nm_kat, SUM( IFNULL(SB.stok, 0 )) stok, IFNULL(laku, 0) laku
FROM barang B
JOIN satuan S ON B.id_sat = S.id_sat
JOIN kategori ON barang.id_kat = kategori.id_kat
LEFT JOIN stok_brg SB ON B.id_brg = SB.id_brg
LEFT JOIN (SELECT B.id_brg, SUM( IFNULL(BL.dibeli, 0)) laku
           FROM barang B
           INNER JOIN brg_laku BL ON B.id_brg = BL.id_brg
           WHERE (a.stok-a.laku) <= 3
           GROUP BY B.id_brg ASC) brg_laku BL ON B.id_brg = BL.id_brg
GROUP BY B.id_brg ASC) a;

Answer 5

你必须首先获得a.stok和a.laku，计算差异，然后将其存储到sql变量中，然后在where子句中使用它。因为mysql不会在select情况下首先计算差异，然后提取相应的行。你必须这样做。我希望这能帮到你

Answer 6

SELECT statement的文档说明：

可以使用select_expr为AS alias_name提供别名。别名用作表达式的列名，可以在GROUP BY，ORDER BY或HAVING子句中使用。

[...]

不允许在WHERE子句中引用列别名，因为在执行WHERE子句时可能尚未确定列值。
  请参阅Section B.5.4.4, "Problems with Column Aliases"。

解决方案很简单：不要在WHERE子句中使用别名，而是使用别名表达式：

SELECT ... (a.stok-a.laku) as difference, ...
...
WHERE a.stok-a.laku <= 3
...

Answer 7

MySQL - 与所有其他数据库一样 - 不允许WHERE子句中的表别名。但是，MySQL扩展了HAVING子句以允许这种过滤。所以，你可以这样做：

SELECT a.id_brg, a.nm_brg, a.jen_sat, a.nm_kat, a.stok, a.laku,
       (a.stok - a.laku) as difference
FROM (SELECT barang.id_brg, barang.nm_brg, jen_sat, nm_kat,
             SUM(COALESCE(stok_brg.stok, 0 )) AS stok, 
             COALESCE( laku, 0 ) AS laku
      FROM barang JOIN
           satuan
           ON barang.id_sat = satuan.id_sat JOIN
           kategori
           ON barang.id_kat = kategori.id_kat LEFT JOIN
           stok_brg
           ON barang.id_brg = stok_brg.id_brg LEFT JOIN
           (SELECT brg_laku.id_brg, SUM(COALESCE(brg_laku.dibeli, 0)) AS laku
            FROM brg_laku
            GROUP BY brg_laku.id_brg
          ) brg_lak
          ON barang.id_brg = brg_laku.id_brg
     GROUP BY barang.id_brg
    ) as a
HAVING difference <= 3;

注意：

我更喜欢COALESCE()到IFNULL()，因为前者是ANSI标准函数。
我简化了最后一个子查询。 JOIN似乎没必要。（可能在某些情况下，但我猜它不是。）
COALESCE()你可能不需要IFNULL() / SUM()。我把它们留在了，但聚合函数中忽略了NULL。

未知的列＆＃39;差异＆＃39; in＆＃39; where子句

7 个答案: