多表连接查询
一些使用数据库的场景中，需要一个查询当中使用到多张表的数据，你可以通过 JOIN 语句将两张或多张表的数据组合在一起。
开始前准备
你需要确认在开始之前，已经完成了以下任务：
已完成单机部署 MatrixOne。
数据准备
-
下载数据集：
https://community-shared-data-1308875761.cos.ap-beijing.myqcloud.com/tpch/tpch-1g.zip -
创建数据库和数据表：
create database d1; use d1; CREATE TABLE NATION ( N_NATIONKEY INTEGER NOT NULL, N_NAME CHAR(25) NOT NULL, N_REGIONKEY INTEGER NOT NULL, N_COMMENT VARCHAR(152), PRIMARY KEY (N_NATIONKEY)); CREATE TABLE REGION ( R_REGIONKEY INTEGER NOT NULL, R_NAME CHAR(25) NOT NULL, R_COMMENT VARCHAR(152), PRIMARY KEY (R_REGIONKEY)); CREATE TABLE PART ( P_PARTKEY INTEGER NOT NULL, P_NAME VARCHAR(55) NOT NULL, P_MFGR CHAR(25) NOT NULL, P_BRAND CHAR(10) NOT NULL, P_TYPE VARCHAR(25) NOT NULL, P_SIZE INTEGER NOT NULL, P_CONTAINER CHAR(10) NOT NULL, P_RETAILPRICE DECIMAL(15,2) NOT NULL, P_COMMENT VARCHAR(23) NOT NULL, PRIMARY KEY (P_PARTKEY)); CREATE TABLE SUPPLIER ( S_SUPPKEY INTEGER NOT NULL, S_NAME CHAR(25) NOT NULL, S_ADDRESS VARCHAR(40) NOT NULL, S_NATIONKEY INTEGER NOT NULL, S_PHONE CHAR(15) NOT NULL, S_ACCTBAL DECIMAL(15,2) NOT NULL, S_COMMENT VARCHAR(101) NOT NULL, PRIMARY KEY (S_SUPPKEY)); CREATE TABLE PARTSUPP ( PS_PARTKEY INTEGER NOT NULL, PS_SUPPKEY INTEGER NOT NULL, PS_AVAILQTY INTEGER NOT NULL, PS_SUPPLYCOST DECIMAL(15,2) NOT NULL, PS_COMMENT VARCHAR(199) NOT NULL, PRIMARY KEY (PS_PARTKEY, PS_SUPPKEY)); CREATE TABLE CUSTOMER ( C_CUSTKEY INTEGER NOT NULL, C_NAME VARCHAR(25) NOT NULL, C_ADDRESS VARCHAR(40) NOT NULL, C_NATIONKEY INTEGER NOT NULL, C_PHONE CHAR(15) NOT NULL, C_ACCTBAL DECIMAL(15,2) NOT NULL, C_MKTSEGMENT CHAR(10) NOT NULL, C_COMMENT VARCHAR(117) NOT NULL, PRIMARY KEY (C_CUSTKEY)); CREATE TABLE ORDERS ( O_ORDERKEY BIGINT NOT NULL, O_CUSTKEY INTEGER NOT NULL, O_ORDERSTATUS CHAR(1) NOT NULL, O_TOTALPRICE DECIMAL(15,2) NOT NULL, O_ORDERDATE DATE NOT NULL, O_ORDERPRIORITY CHAR(15) NOT NULL, O_CLERK CHAR(15) NOT NULL, O_SHIPPRIORITY INTEGER NOT NULL, O_COMMENT VARCHAR(79) NOT NULL, PRIMARY KEY (O_ORDERKEY)); CREATE TABLE LINEITEM ( L_ORDERKEY BIGINT NOT NULL, L_PARTKEY INTEGER NOT NULL, L_SUPPKEY INTEGER NOT NULL, L_LINENUMBER INTEGER NOT NULL, L_QUANTITY DECIMAL(15,2) NOT NULL, L_EXTENDEDPRICE DECIMAL(15,2) NOT NULL, L_DISCOUNT DECIMAL(15,2) NOT NULL, L_TAX DECIMAL(15,2) NOT NULL, L_RETURNFLAG CHAR(1) NOT NULL, L_LINESTATUS CHAR(1) NOT NULL, L_SHIPDATE DATE NOT NULL, L_COMMITDATE DATE NOT NULL, L_RECEIPTDATE DATE NOT NULL, L_SHIPINSTRUCT CHAR(25) NOT NULL, L_SHIPMODE CHAR(10) NOT NULL, L_COMMENT VARCHAR(44) NOT NULL, PRIMARY KEY (L_ORDERKEY, L_LINENUMBER)); -
把数据导入到数据表中：
load data infile '/YOUR_TPCH_DATA_PATH/nation.tbl' into table NATION FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n'; load data infile '/YOUR_TPCH_DATA_PATH/region.tbl' into table REGION FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n'; load data infile '/YOUR_TPCH_DATA_PATH/part.tbl' into table PART FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n'; load data infile '/YOUR_TPCH_DATA_PATH/supplier.tbl' into table SUPPLIER FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n'; load data infile '/YOUR_TPCH_DATA_PATH/partsupp.tbl' into table PARTSUPP FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n'; load data infile '/YOUR_TPCH_DATA_PATH/orders.tbl' into table ORDERS FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n'; load data infile '/YOUR_TPCH_DATA_PATH/customer.tbl' into table CUSTOMER FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n'; load data infile '/YOUR_TPCH_DATA_PATH/lineitem.tbl' into table LINEITEM FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n';
现在你可以使用这些数据进行查询。
Join 类型
内连接
内连接的连接结果只返回匹配连接条件的行。
| 语法 | 图示 |
|---|---|
| SELECT |
 |
内连接有两种书写方式，在结果上是完全等价的：
mysql> SELECT
l_orderkey,
SUM(l_extendedprice * (1 - l_discount)) AS revenue,
o_orderdate,
o_shippriority
FROM
CUSTOMER,
ORDERS,
LINEITEM
WHERE
c_mktsegment = 'BUILDING'
AND c_custkey = o_custkey
AND l_orderkey = o_orderkey
AND o_orderdate < DATE '1995-03-15'
AND l_shipdate > DATE '1995-03-15'
GROUP BY l_orderkey , o_orderdate , o_shippriority
ORDER BY revenue DESC , o_orderdate
LIMIT 10;
+------------+---------------------+-------------+----------------+
| l_orderkey | revenue | o_orderdate | o_shippriority |
+------------+---------------------+-------------+----------------+
| 2456423 | 406181.011100000000 | 1995-03-05 | 0 |
| 3459808 | 405838.698900000000 | 1995-03-04 | 0 |
| 492164 | 390324.061000000000 | 1995-02-19 | 0 |
| 1188320 | 384537.935900000000 | 1995-03-09 | 0 |
| 2435712 | 378673.055800000000 | 1995-02-26 | 0 |
| 4878020 | 378376.795200000000 | 1995-03-12 | 0 |
| 5521732 | 375153.921500000000 | 1995-03-13 | 0 |
| 2628192 | 373133.309400000000 | 1995-02-22 | 0 |
| 993600 | 371407.459500000000 | 1995-03-05 | 0 |
| 2300070 | 367371.145200000000 | 1995-03-13 | 0 |
+------------+---------------------+-------------+----------------+
10 rows in set (0.20 sec)
写成 Join 的形式，语法如下：
mysql> SELECT
l_orderkey,
SUM(l_extendedprice * (1 - l_discount)) AS revenue,
o_orderdate,
o_shippriority
FROM
CUSTOMER
join ORDERS on c_custkey = o_custkey
join LINEITEM on l_orderkey = o_orderkey
WHERE
c_mktsegment = 'BUILDING'
AND o_orderdate < DATE '1995-03-15'
AND l_shipdate > DATE '1995-03-15'
GROUP BY l_orderkey , o_orderdate , o_shippriority
ORDER BY revenue DESC , o_orderdate
LIMIT 10;
+------------+---------------------+-------------+----------------+
| l_orderkey | revenue | o_orderdate | o_shippriority |
+------------+---------------------+-------------+----------------+
| 2456423 | 406181.011100000000 | 1995-03-05 | 0 |
| 3459808 | 405838.698900000000 | 1995-03-04 | 0 |
| 492164 | 390324.061000000000 | 1995-02-19 | 0 |
| 1188320 | 384537.935900000000 | 1995-03-09 | 0 |
| 2435712 | 378673.055800000000 | 1995-02-26 | 0 |
| 4878020 | 378376.795200000000 | 1995-03-12 | 0 |
| 5521732 | 375153.921500000000 | 1995-03-13 | 0 |
| 2628192 | 373133.309400000000 | 1995-02-22 | 0 |
| 993600 | 371407.459500000000 | 1995-03-05 | 0 |
| 2300070 | 367371.145200000000 | 1995-03-13 | 0 |
+------------+---------------------+-------------+----------------+
10 rows in set (0.20 sec)
外连接
外连接又分为左连接、右连接，两者之间是可以实现等价语义的：
LEFT JOIN
左外连接会返回左表中的所有数据行，以及右表当中能够匹配连接条件的值，如果在右表当中没有找到能够匹配的行，则使用 NULL 填充。
| 语法 | 图示 |
|---|---|
| SELECT |
 |
| SELECT |
 |
RIGHT JOIN
右外连接返回右表中的所有记录，以及左表当中能够匹配连接条件的值，没有匹配的值则使用 NULL 填充。
| 语法 | 图示 |
|---|---|
| SELECT |
 |
| SELECT |
 |
语句示例如下：
SELECT
c_custkey, COUNT(o_orderkey) AS c_count
FROM
CUSTOMER
LEFT OUTER JOIN ORDERS ON (c_custkey = o_custkey
AND o_comment NOT LIKE '%special%requests%')
GROUP BY c_custkey limit 10;
+-----------+---------+
| c_custkey | c_count |
+-----------+---------+
| 147457 | 16 |
| 147458 | 7 |
| 147459 | 0 |
| 147460 | 16 |
| 147461 | 7 |
| 147462 | 0 |
| 147463 | 14 |
| 147464 | 11 |
| 147465 | 0 |
| 147466 | 17 |
+-----------+---------+
10 rows in set (0.93 sec)
或者：
SELECT
c_custkey, COUNT(o_orderkey) AS c_count
FROM
ORDERS
RIGHT OUTER JOIN CUSTOMER ON (c_custkey = o_custkey
AND o_comment NOT LIKE '%special%requests%')
GROUP BY c_custkey limit 10;
+-----------+---------+
| c_custkey | c_count |
+-----------+---------+
| 147457 | 16 |
| 147458 | 7 |
| 147459 | 0 |
| 147460 | 16 |
| 147461 | 7 |
| 147462 | 0 |
| 147463 | 14 |
| 147464 | 11 |
| 147465 | 0 |
| 147466 | 17 |
+-----------+---------+
10 rows in set (0.93 sec)
全连接
全连接是左右外连接的并集。连接表包含被连接的表的所有记录，如果缺少匹配的记录，即以 NULL 填充。
SELECT
c_custkey, COUNT(o_orderkey) AS c_count
FROM
CUSTOMER
FULL JOIN ORDERS ON (c_custkey = o_custkey
AND o_comment NOT LIKE '%special%requests%')
GROUP BY c_custkey limit 10;
+-----------+---------+
| c_custkey | c_count |
+-----------+---------+
| 1 | 6 |
| 2 | 7 |
| 4 | 20 |
| 5 | 4 |
| 7 | 16 |
| 8 | 13 |
| 10 | 20 |
| 11 | 13 |
| 13 | 18 |
| 14 | 9 |
+-----------+---------+
10 rows in set (0.77 sec)
全连接同样可以通过改写的方式获得相同的语义：
SELECT
c_custkey, COUNT(o_orderkey) AS c_count
FROM
CUSTOMER
LEFT OUTER JOIN ORDERS ON (c_custkey = o_custkey
AND o_comment NOT LIKE '%special%requests%')
GROUP BY c_custkey
UNION
SELECT
c_custkey, COUNT(o_orderkey) AS c_count
FROM
CUSTOMER
LEFT OUTER JOIN ORDERS ON (c_custkey = o_custkey
AND o_comment NOT LIKE '%special%requests%')
WHERE c_custkey IS NULL
GROUP BY c_custkey
limit 10;
+-----------+---------+
| c_custkey | c_count |
+-----------+---------+
| 147457 | 16 |
| 147458 | 7 |
| 147459 | 0 |
| 147460 | 16 |
| 147461 | 7 |
| 147462 | 0 |
| 147463 | 14 |
| 147464 | 11 |
| 147465 | 0 |
| 147466 | 17 |
+-----------+---------+
10 rows in set (1.09 sec)
隐式连接
在 SQL 语句当中，除了使用 JOIN，也可以通过 FROM t1, t2 子句来连接两张或多张表，通过 WHERE t1.id = t2.id 子句来指定连接的条件。