条件连接 | SQL |优化性能并减少数量。加入数

Question

我有以下表格：

t1:

create table t1 (auth_date string,
                 auth_nbr int,
                 debit_date string,
                 debit_nbr int,
                 txn_dttm string,
                 iss_id string,
                 audit_num int);

insert into t1 values 
('01-05-2021',12,null,null,'01-05-2021','b',124),
(null,null,'02-05-2021',13,'02-05-2021','c',125),
('02-05-2021',14,'02-05-2021',14,'02-05-2021','d',126);

t2:

create table t2 (txn_amt int,txn_dttm string,iss_id string,audit_num int);

insert into t2 values 
(2000,'01-05-2021','b',124),
(2500,'02-05-2021','c',125),
(1000,'02-05-2021','d',126);

我想要我的输出：

dw_date|dw_nbr|amt
01-05-2021|12|2000
02-05-2021|13|2500
02-05-2021|14|1000

我有以下查询。但由于加入是一项繁重的操作，我只想将其缩小到 1 个加入。但是我在这两种情况下的加入是不同的条件，即在第一个条件中加入是在 3 个列上，而在另一个加入是在 2 个列上。我想找到一种方法来实现所需的输出。条件连接。或者别的什么。 从t2表中，我只需要相关的txn_amt。

select dw_date,dw_nbr,amt 
from (select t1.auth_date,t1.auth_nbr,t2.amt from t1 join t2 on t1.txn_dttm=t2.txn_dttm and t1.iss_id=t2.iss_id and t1.audit_num=t2.audit_num 
where auth_date is not null and auth_nbr is not null and debit_date is null and debit_nbr is null)a 
union all 
select dw_date,dw_nbr,amt 
from (select t1.debit_date,t1.debit_nbr,t2.amt from t1 join t2 on t1.txn_dttm=t2.txn_dttm and t1.audit_num=t2.audit_num 
where debit_date is not null and debit_nbr is not null)a;

Answer 1

请检查这个。由于使用的是最新版本的 MYSQL，因此请使用 CTE 以避免多次使用大表。

-- MySQL(v5.8)
WITH a_cte AS (
    SELECT t1.auth_date, t1.auth_nbr, t2.txn_amt
         , t1.debit_date, t1.debit_nbr
         , CASE WHEN t1.iss_id = t2.iss_id
                   THEN 1
                ELSE 0
           END iss_id
    FROM t1
    INNER JOIN t2
            ON t1.txn_dttm = t2.txn_dttm 
           AND t1.audit_num = t2.audit_num 
), b_cte AS (
    SELECT auth_date AS dw_date
         , auth_nbr AS dw_nbr
         , txn_amt AS amt
    FROM a_cte
    WHERE iss_id = 1
        AND auth_date is not null 
        AND auth_nbr is not null 
        AND debit_date is null 
        AND debit_nbr is null
    
    UNION ALL
    
    SELECT debit_date AS dw_date
         , debit_nbr AS dw_nbr
         , txn_amt AS amt
    FROM a_cte
    WHERE debit_date is not null 
        AND debit_nbr is not null 
)
SELECT *
FROM b_cte;

请查看网址https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=1a482589e2cdc1f6b288c93f88150fa5