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This article mainly introduces the relevant knowledge of "what is the conditional query method of count () in mybatis". The editor shows you the operation process through an actual case, and the operation method is simple, fast and practical. I hope that this article "what is the method of conditional query of count () in mybatis" can help you solve the problem.

Mybatis count () queries 1 and sql count () functions by condition

The count () function returns the number of rows that match the specified criteria.

Sql count (column_name) syntax:

The number of values returned by the count (column_name) function for the specified column (null) is not counted.

Select count (column_name) from table_name

Sql count (*) syntax:

The count (*) function returns the number of records in the table.

Select count (*) from table_name

Sql count (distinct column_name) syntax:

The count (distinct column_name) function returns the number of different values for the specified column.

Select count (distinct column_name) from table_name

For example, the following table: table_aid

+-+ | aid | site_id | count | date | +-+ | 1 | 1 | 45 | 2016-05-10 | 2 | 3 | 100 | 2016-05- | 13 | 3 | 1 | 2016 | 2016-05-14 | 4 | 2 | 10 | 2016-05-14 | 5 | 5 | 20 | 2016-05-14 | 6 | 4 | 13 | 2016-05-15 | 7 | 3 | 2016-05-15 | 8 | 5 | 545 | 2016-05-16 | 9 | 3 | 2016-05-17 | | | +-+

Execute the sql statement:

/ / number of specified columns under specific conditions select count (count) as nums from table_aidwhere site_id = 3Universe / output result: Nums value is: 521 / / calculate the total number of records in table_aid select count (*) as nums from table_aid// output result: Nums value is: 9 / / number of different values of specified column select count (distinct site_id) as nums from table_aid// output result: Nums value is: 52, count () in mybatis query by condition

Task description: two fields in the database are

1. Site: station,

2. Status: the value of status,status is success or fail.

Now the requirement is to group records by site, and count the number of status as success and the number as fail.

Mybatis Code:

Select rfr.station, count (rfr.status='success' or null) as successNum, count (rfr.status='fail' or null) as failNum, count (1) as totalNum from rec_file_report rfr GROUP BY station

The test results are as follows:

{

"failNum": 2

"totalNum": 73

"successNum": 71

"station": "admin"

}

{

"failNum": 26

TotalNum: 521

"successNum": 495

"station": "changjiu.shao@wisdom56.com"

}

When querying, use count (*), total is 1, and the result is 0

When using the count (*) query, it is found that the total returned by the mybatis log printed on console is 1, but the actual situation should be 0, and the returned data is also 0.

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