Introduction to MySQL WITH Clause
MySQL WITH clause is used to define the CTE (Common table expressions). A common table expression is a named temporary result set that can be used multiple times. The CTE can be defined using WITH clause and can have one or more sub-clauses separated by a comma. The sub-clauses that are defined consists of each result set associated with a name to it. CTE can be used in other CTE’s. We also have recursive CTE which will be referred to itself. The result set exists only within the scope of a single statement as SELECT, INSERT, UPDATE or DELETE.
In this session let us see how the CTE will be defined using the WITH clause along with an example.
Syntax of MySQL WITH
Now let us consider the syntax of declaring the CTE using WITH clause:
1. Declaration of Single CTE
Syntax:
WITH <CTE NAME><COLUMN LIST > AS
<
QUERY STATEMENT
>
SELECT * FROM <CTE NAME>;
2. Declaration of Multiple CTE
Syntax:
WITH <CTE NAME1><COLUMN LIST > AS
<
QUERY STATEMENT
>
, <CTE NAME2><COLUMN LIST > AS
<
QUERY STATEMENT
>
SELECT * FROM <CTE NAME1> join <CTE NAME2> ON <Condition>;
WITH clause can be used in the beginning as:
- WITH … SELECT …
- WITH … UPDATE …
- WITH … DELETE …
WITH statement can immediately precede as below:
- CREATE TABLE … WITH … SELECT …
- CREATE VIEW … WITH … SELECT …
- INSERT … WITH … SELECT …
- REPLACE … WITH … SELECT …
- DECLARE CURSOR … WITH … SELECT …
- EXPLAIN … WITH … SELECT …
How WITH Clause Works in MySQL?
Now let us consider the tables apply the CTE concept using the WITH clause:
1. Let us create a Table and use the above Syntax format and insert Data into the Table.
create table Order_detail
(
shop_id int,
product_id int,
brand_id int,
Shop_name varchar(20),
quantity int,
price int
);
2. Now let us insert Data into the Table.
insert into Order_detail (shop_id, product_id, brand_id, Shop_name, quantity, price)
values (1,1,1,'Kellogs',45,45);
insert into Order_detail (shop_id, product_id, brand_id, Shop_name, quantity, price)
values (2,7,5,'Fantasy Store',75,145);
insert into Order_detail (shop_id, product_id, brand_id, Shop_name, quantity, price)
values (3,3,2,'Laxshmi store',65,85);
insert into Order_detail (shop_id, product_id, brand_id, Shop_name, quantity, price)
values (4,4,7,'General store',25,65);
insert into Order_detail (shop_id, product_id, brand_id, Shop_name, quantity, price)
values (5,5,8,'Corn store',35,75);
Query:
select * from Order_detail;
Output:
3. Now let us Perform the Simple CTE Creation on the above Table.
Query:
With CTE_Orders_Store AS
(
Select shop_id,
product_id,
brand_id,
shop_name,
quantity
from order_detail where UPPER(shop_name) like '%store%'
)
Select * from CTE_Orders_Store where quantity> 50;
Output:
Explanation: Here we are finding the shops which has stored in their “shop_name” and the number of products sold greater than 50.
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4. Now let us Perform another Simple CTE on the above Table.
Query:
With CTE_Orders_quantity AS
(
Select shop_id,
product_id,
brand_id,
shop_name,
quantity
from order_detail where quantity> 30
)
Select * from CTE_Orders_quantity where shop_idin( 2, 1);
Output:
Explanation: Here we are finding the shop’s which has quantity sold > 30 and then we are filtering the rest and bring only the shop_id that are (2, 1).
5. Now let us Consider the above Created table “order_detail” as well create another Table as below.
Query:
create table Details_People
(
id int,
name varchar(20),
location varchar(20),
pincodeint,
product_idint
);
6. Insert the Below Rows into the Table as below.
Query:
insert into DETAILS_PEOPLE values (1, 'Sam', 'MP', 564321,1);
insert into DETAILS_PEOPLE values (2, 'Sohan', 'Bangalore', 523321,7);
insert into DETAILS_PEOPLE values (3, 'Will', 'Tamilnadu', 523021,3);
insert into DETAILS_PEOPLE values (4, 'Ben', 'UP', 564000,3);
insert into DETAILS_PEOPLE values (5, 'Hamington', 'UP', 564000,4);
insert into DETAILS_PEOPLE values (6, 'Ji eun', 'Bangalore', 523321,2);
insert into DETAILS_PEOPLE values (7, 'Jimin', 'UP', 564000,5);
insert into DETAILS_PEOPLE values (8, 'Jk', 'Bangalore', 523321,4);
insert into DETAILS_PEOPLE values (9, 'V', 'AP', 590001,5);
insert into DETAILS_PEOPLE values (10, 'Jhope', 'Bangalore', 523321,1);
7. Now let us Select the Columns from the Table
Query:
Select * from Details_People;
Output:
8. Now let us perform the Complex CTE Between the two Tables.
Query:
With CTE_Orders_Store AS
(
Select shop_id,
product_id,
brand_id,
shop_name,
quantity
from order_detail where UPPER(shop_name) like '%store%'
)
Select * from CTE_Orders_Stores
JOIN details_people p
ON s.product_id=p.product_id
where quantity> 50;
Output:
Explanation: Here in the above query we are finding the shop’s which has stored in their “shop_name” and the number of products sold greater than 50. The output of the CTE we have joined with the “details_people” and got the output.
Query:
With CTE_Orders_quantity AS
(
Select shop_id,
product_id,
brand_id,
shop_name,
quantity
from order_detail where quantity> 30
)
Select * from CTE_Orders_quantity s
JOIN details_people p
ON s.product_id=p.product_id
where shop_idin( 2, 1);
Output:
Explanation: Here we are finding the shop’s which has quantity sold > 30 and then we are filtering the rest and bring only the shop_id that are (2, 1) then join it with the “details_people” table.
9. Now let us see the RECURSIVE CTE
Query:
WITH RECURSIVE REC_cte AS
(
SELECT 1 AS A, 1 AS B, -1 AS C
UNION ALL
SELECT A + 1, B * 2, C * 2 FROM REC_cte WHERE A < 5
)
SELECT * FROM REC_cte;
Output:
Conclusion
- MySQL WITH clause is used to define the CTE (Common table expressions). A common table expression is a named temporary result set that can be used multiple times.
- The CTE can be defined using WITH clause and can have one or more sub-clauses separated by a comma.
- The sub-clauses that are defined consists of each result set associated with a name to it. CTE can be used in another CTE’s. We also have recursive CTE which will be referred to itself.
- The result set exists only within the scope of the single statement as SELECT, INSERT, UPDATE or DELETE
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