mysql - 保留原表mysql的同时唯一join

Question

我想在sql中加入三个表。table1 和 table2 需要在键符号上连接，但是 table1 中的符号需要在连接之前进行编辑。

三连：

SELECT table1.symbol, table1.risk_factor, table1.risk_factor_name, table1.type, table1.position, table3.`Position dif ex corr`, table1.haircut
FROM `Positions_EOD` table1
LEFT JOIN `positions1` table2 ON table1.symbol = table2.symbol
LEFT JOIN (SELECT * FROM `Final_Pos` WHERE business_date = '2020-04-01' AND `Position check` = 'Correct') table3 ON table2.isin = LEFT(table3.VT_id, INSTR(table3.VT_id, '_') - 1)
WHERE table1.business_date = '2020-04-01' AND table2.business_date = '2020-04-01' AND table2.legal_entity = 'HK' AND table1.symbol LIKE 'ES%'

在加入table1之前，需要这样编辑：

SELECT 
CASE
    WHEN (`type` = 'ST') THEN symbol
    WHEN (`type` = 'FU') THEN LEFT(REPLACE(symbol,' ', ''), LENGTH(REPLACE(symbol,' ', ''))-2)
END AS 'symbol'
FROM `Positions_EOD`

如何编辑 table1 连接，以便在加入之前编辑 table1 中的符号？

标签： mysqlsql

Answer 1

在 ON 子句中使用 CASE 表达式：

SELECT table1.symbol, table1.risk_factor, table1.risk_factor_name, table1.type, table1.position, table3.`Position dif ex corr`, table1.haircut
FROM `Positions_EOD` table1 LEFT JOIN `positions1` table2
ON CASE
    WHEN (table1.`type` = 'ST') THEN table1.symbol
    WHEN (table1.`type` = 'FU') THEN LEFT(REPLACE(table1.symbol,' ', ''), LENGTH(REPLACE(table1.symbol,' ', ''))-2)
END = table2.symbol
..................................