CROSS/OUTER 申请 MySQL
CROSS/OUTER APPLY in MySQL
我需要在 MySQL(EC2 RDS MySQL 实例)中使用 CROSS APPLY。
看起来 MySQL 无法识别 CROSS APPLY 语法。有人可以帮我吗?
这是查询。
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD
CROSS APPLY (
SELECT TOP 1 ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
) ORD_HIST
最接近的直接近似是一个以相关子查询为谓词的连接。
SELECT
ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HISTORY.VALUE
FROM
ORD
INNER JOIN
ORD_HISTORY
ON ORD_HISTORY.<PRIMARY_KEY>
=
(SELECT ORD_HISTORY.<PRIMARY_KEY>
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
)
然而,在您的情况下,您只需要来自目标 table 的一个字段。这意味着您可以直接在 SELECT 语句中使用相关子查询。
SELECT
ORD.ID
,ORD.NAME
,ORD.DATE
,(SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) AS VALUE
FROM
ORD
从 MySQL 8.0.14 开始,您可以使用 LATERAL
:
A derived table now may be preceded by the LATERAL keyword to specify that it is permitted to refer to (depend on) columns of preceding tables in the same FROM clause. A derived table specified with LATERAL can occur only in a FROM clause, either in a list of tables separated with commas or in a join specification (JOIN, INNER JOIN, CROSS JOIN, LEFT [OUTER] JOIN, or RIGHT [OUTER] JOIN). Lateral derived tables make possible certain SQL operations that cannot be done with nonlateral derived tables or that require less-efficient workarounds
CROSS APPLY () <=> ,LATERAL ()
OUTER APPLY () <=> LEFT JOIN LATERAL () ON 1=1
Support for LATERAL derived tables added to MySQL 8.0.14
在这种情况下:
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD,
LATERAL (
SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) ORD_HIST;
如果相关子查询没有return 任何行,主查询的主行将被跳过。在这种情况下,应该使用LEFT JOIN LATERAL
。
基于@lujas szozda 的回答:
对于交叉应用:
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD JOIN
LATERAL (
SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) ORD_HIST ON 1=1
/* ON 1=1 is just a trick to join to whatever the LATERAL returns */
对于外部应用:
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD LEFT JOIN
LATERAL (
SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) ORD_HIST ON 1=1
/* ON 1=1 is just a trick to join to whatever the LATERAL returns */
我需要在 MySQL(EC2 RDS MySQL 实例)中使用 CROSS APPLY。 看起来 MySQL 无法识别 CROSS APPLY 语法。有人可以帮我吗?
这是查询。
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD
CROSS APPLY (
SELECT TOP 1 ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
) ORD_HIST
最接近的直接近似是一个以相关子查询为谓词的连接。
SELECT
ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HISTORY.VALUE
FROM
ORD
INNER JOIN
ORD_HISTORY
ON ORD_HISTORY.<PRIMARY_KEY>
=
(SELECT ORD_HISTORY.<PRIMARY_KEY>
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
)
然而,在您的情况下,您只需要来自目标 table 的一个字段。这意味着您可以直接在 SELECT 语句中使用相关子查询。
SELECT
ORD.ID
,ORD.NAME
,ORD.DATE
,(SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) AS VALUE
FROM
ORD
从 MySQL 8.0.14 开始,您可以使用 LATERAL
:
A derived table now may be preceded by the LATERAL keyword to specify that it is permitted to refer to (depend on) columns of preceding tables in the same FROM clause. A derived table specified with LATERAL can occur only in a FROM clause, either in a list of tables separated with commas or in a join specification (JOIN, INNER JOIN, CROSS JOIN, LEFT [OUTER] JOIN, or RIGHT [OUTER] JOIN). Lateral derived tables make possible certain SQL operations that cannot be done with nonlateral derived tables or that require less-efficient workarounds
CROSS APPLY () <=> ,LATERAL ()
OUTER APPLY () <=> LEFT JOIN LATERAL () ON 1=1
Support for LATERAL derived tables added to MySQL 8.0.14
在这种情况下:
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD,
LATERAL (
SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) ORD_HIST;
如果相关子查询没有return 任何行,主查询的主行将被跳过。在这种情况下,应该使用LEFT JOIN LATERAL
。
基于@lujas szozda 的回答:
对于交叉应用:
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD JOIN
LATERAL (
SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) ORD_HIST ON 1=1
/* ON 1=1 is just a trick to join to whatever the LATERAL returns */
对于外部应用:
SELECT ORD.ID
,ORD.NAME
,ORD.DATE
,ORD_HIST.VALUE
FROM ORD LEFT JOIN
LATERAL (
SELECT ORD_HISTORY.VALUE
FROM ORD_HISTORY
WHERE ORD.ID = ORD_HISTORY.ID
AND ORD.DATE <= ORD_HISTORY.DATE
ORDER BY ORD_HISTORY.DATE DESC
LIMIT 1
) ORD_HIST ON 1=1
/* ON 1=1 is just a trick to join to whatever the LATERAL returns */