How to query and count the quantity in mysql

In mysql, you can use the SELECT statement to query data, and use the COUNT() function to count the number of query results. The syntax is "SELECT COUNT(*) FROM table name [...];" or "SELECT COUNT (field name) FROM table name[...];".

The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.

In mysql, you can use the SELECT statement to query data, and use the COUNT() function to count the number of query results. The syntax format of

SELECTis as follows:

SELECT {* | <字段列名>} [ FROM <表 1>, <表 2>… [WHERE <表达式> [GROUP BY  [HAVING  [{ }…]] [ORDER BY ] [LIMIT[,] ] ]

Among them, the meaning of each clause is as follows:

• {*|b44f51d0b443c93502271d3d391e4df2}A field list containing the asterisk wildcard character, indicating the name of the field to be queried.

• ##05cee8b6ad5efd33489a0be0260a7bbc, a31a6b5c4a9ac86f75409c3950db0e23…, Table 1 and Table 2 represent the source of query data, which can be single or multiple.

• WHERE ffbeece48539e6983ff3249db04f27c9is optional. If selected, the query data must meet the query conditions.

• GROUP BY3b26370eed070b4e2af74808aa8f2dee, this clause tells MySQL how to display the queried data and group it according to the specified field.

• ##[ORDER BY0f5333100010744a1571ca8552350494]

  , this clause tells MySQL in what order to display the queried data, the sorting that can be done is in ascending order ( ASC) and descending (DESC), which is ascending by default.

##[LIMIT[ab76cfca1a1dc7ff1291dcdf873f72ec,]bc984d207842008469e14f06321b6461]
• , this clause tells MySQL to display the number of queried data items each time.

The function counts the total number of record rows contained in the data table, or returns the number of data rows contained in the column based on the query results

COUNT(*)
• Calculate the total number of rows in the table, regardless of whether a column has a value or a null value.

COUNT(expression)
• Counts the number of rows that do not contain a

  NULLvalue.

COUNT(DISTINCT expression)
• Returns the number of unique rows that do not contain a

  NULLvalue## The return type of the #COUNT() function is

  BIGINT
. If no matching row is found, the COUNT() function returns

.MySQL COUNT exampleLet’s create a new table named

and insert some sample data.

USE testdb; -- create a demos table CREATE TABLE IF NOT EXISTS demos( id int auto_increment primary key, val int ); -- insert some sample data INSERT INTO demos(val) VALUES(1),(1),(2),(2),(NULL),(3),(4),(NULL),(5); -- select data from demos table SELECT * FROM demos;

Execute the above query statement and get the following results-

+----+------+ | id | val | +----+------+ | 1 | 1 | | 2 | 1 | | 3 | 2 | | 4 | 2 | | 5 | NULL | | 6 | 3 | | 7 | 4 | | 8 | NULL | | 9 | 5 | +----+------+ 9 rows in set

table, please use

function, as shown below:

mysql> SELECT COUNT(*) FROM demos; +----------+ | COUNT(*) | +----------+ | 9 | +----------+ 1 row in set

columns that contain values equal to ## For rows #2, use the following query:

mysql> SELECT COUNT(*) FROM demos WHERE val = 2; +----------+ | COUNT(*) | +----------+ | 2 | +----------+ 1 row in set

COUNTfunction counts All rows whosevalcolumn contains only non-NULLvalues. See the following query: TwoNULLvalues in the

SELECT COUNT(*) FROM demos WHERE val = 2;

To count the unique rows in thedemostable, you can add theDISTINCT

COUNTfunction, as in the following query statement:

SELECT COUNT(DISTINCT val) FROM demos;

mysql> SELECT COUNT(DISTINCT val) FROM demos; +---------------------+ | COUNT(DISTINCT val) | +---------------------+ | 5 | +---------------------+ 1 row in set

2

in the count NULLvalue.MySQL COUNT with GROUP BYWe often use theCOUNT

GROUP BY

productstable below -

mysql> desc products; +--------------------+---------------+------+-----+---------+------------------+ | Field | Type | Null | Key | Default | Extra | +--------------------+---------------+------+-----+---------+------------------+ | productCode | varchar(15) | NO | PRI | | | | productName | varchar(70) | NO | MUL | NULL | | | productLine | varchar(50) | NO | MUL | NULL | | | productScale | varchar(10) | NO | | NULL | | | productVendor | varchar(50) | NO | | NULL | | | productDescription | text | NO | | NULL | | | quantityInStock | smallint(6) | NO | | NULL | | | buyPrice | decimal(10,2) | NO | | NULL | | | MSRP | decimal(10,2) | NO | | NULL | | | stockValue | double | YES | | NULL | STORED GENERATED | +--------------------+---------------+------+-----+---------+------------------+ 10 rows in set

SELECT productline, count(*) FROM products GROUP BY productline;

mysql> SELECT productline, count(*) FROM products GROUP BY productline; +------------------+----------+ | productline | count(*) | +------------------+----------+ | Classic Cars | 38 | | Motorcycles | 13 | | Planes | 12 | | Ships | 9 | | Trains | 3 | | Trucks and Buses | 11 | | Vintage Cars | 24 | +------------------+----------+ 7 rows in set

SELECT productvendor, count(*) FROM products GROUP BY productvendor;

mysql> SELECT productvendor, count(*) FROM products GROUP BY productvendor; +---------------------------+----------+ | productvendor | count(*) | +---------------------------+----------+ | Autoart Studio Design | 8 | | Carousel DieCast Legends | 9 | | Classic Metal Creations | 10 | | Exoto Designs | 9 | | Gearbox Collectibles | 9 | | Highway 66 Mini Classics | 9 | | Min Lin Diecast | 8 | | Motor City Art Classics | 9 | | Red Start Diecast | 7 | | Second Gear Diecast | 8 | | Studio M Art Models | 8 | | Unimax Art Galleries | 8 | | Welly Diecast Productions | 8 | +---------------------------+----------+ 13 rows in set

9

HAVING

COUNTfunction, as shown in the following query statement:

SELECT productvendor, count(*) FROM products GROUP BY productvendor HAVING count(*) >= 9;

mysql> SELECT productvendor, count(*) FROM products GROUP BY productvendor HAVING count(*) >= 9; +--------------------------+----------+ | productvendor | count(*) | +--------------------------+----------+ | Carousel DieCast Legends | 9 | | Classic Metal Creations | 10 | | Exoto Designs | 9 | | Gearbox Collectibles | 9 | | Highway 66 Mini Classics | 9 | | Motor City Art Classics | 9 | +--------------------------+----------+ 6 rows in set

function, such as

,

,CASE, etc. to count rows whose values match the condition.For example, the following query can find how many canceled, suspended and disputed orders:

SELECT COUNT(IF(status='Cancelled',1, NULL)) 'Cancelled', COUNT(IF(status='On Hold',1, NULL)) 'On Hold', COUNT(IF(status='Disputed',1, NULL)) 'Disputed' FROM orders;

mysql> SELECT COUNT(IF(status='Cancelled',1, NULL)) 'Cancelled', COUNT(IF(status='On Hold',1, NULL)) 'On Hold', COUNT(IF(status='Disputed',1, NULL)) 'Disputed' FROM orders; +-----------+---------+----------+ | Cancelled | On Hold | Disputed | +-----------+---------+----------+ | 6 | 4 | 3 | +-----------+---------+----------+ 1 row in set

, otherwise

will be returned. The

function only counts1, notNULLvalues, so the query returns the number of orders based on the corresponding status.[Related recommendations:mysql video tutorial]

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