SQL

Question

我有两个不共享主键的表（A 和 B）。我需要某种连接，其中对于 Table A 中的每一行，如果 date_B < date_A[=25=，我必须添加 Table B 行].

*日期格式：yyyy-mm-dd

Table一个

+-------+-----+-----------+ | id_A | op_A| date_A | +-------+-----+-----------+ | 1 | 0 | 2018-10-01| | 2 | 0 | 2018-12-31| +-------+-----+-----------+

Table B

+-----+--------+-------------+ | id_b| other | date_B | +-----+--------+-------------+ | a | 8 | 2018-09-01 | | b | 90 | 2018-12-01 | +-----+--------+-------------+

正确结果：

+-----+-----+-----------+-----+--------+-------------+ | id_A| op_A| date_A | id_B| other | date_B | +-----+-----+-----------+-----+--------+-------------+ | 1 | 0 | 2018-10-01| a | 8 | 2018-09-01 | | 2 | 0 | 2018-12-31| a | 8 | 2018-09-01 | | 2 | 0 | 2018-12-31| b | 90 | 2018-12-01 | +-----+-----+-----------+-----+--------+-------------+

Answer 1

这个查询应该会给你你想要的结果：

SELECT *
FROM TableA a
JOIN TableB b ON b.date_B < a.date_A

输出：

id_A    op_A    date_A      id_b    other   date_B
1       0       2018-10-01  a       8       2018-09-01
2       0       2018-12-31  a       8       2018-09-01
2       0       2018-12-31  b       90      2018-12-01

Demo on SQLFiddle

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