A must see for software testers!Database knowledge MySQL query statement Daquan

As a tester, it is indispensable to master the common operations of the database. The following is a mysql query statement to sort out some related grammar knowledge.

This article mainly includes two aspects

·Commonly used sql syntax

·How to associate with sql in the development code

Case code:

`

select a.blastid,d.apptime,a.charge_approve,

a.blast_batch,

a.plan_blast_time,

a.exe_plan_id,

a.import_flag,

a.rig_type,.......

case when (select "count"(*) from bla_geology_info geo where a.blast_id=geo.blast_id and geo.delete_flag=0)>0

then 'true' else 'false'

END as isShowFlag

from bla_blast_info a

left join exe_plan_month b

on a.exe_plan_id = b.exe_plan_id

left join sys_user c

on a.dynamite_user = c.user_id

left join (select blast_id,isagree,idea,create_time as app_time from bla_charge_approve where delete_flag = '0') d

on a.blast_id = d.blast_id

WHERE a.blast_type=1 AND a.blast_status > '3' AND a.blast_status < '8' AND a.charge_approve> '1' AND a.delete_flag = '0' ORDER BY cast(a.charge_approveas numeric) ASC , d.app_time DESC , a.create_time DESC

`

A commonly used sql syntax

1. The query statement select xxxx from table name indicates which table to query from.The content after select is divided by .

2. select xxxx from table name alias, indicating that this table is replaced by an alias, such as a, b, c, etc. in the previous statement

3.case when then xx, else xxx, end as isShowFlag means that the statement after then is executed when the condition is met, otherwise the statement after the else is executed,

eg case when (select "count"(*) from blageologyinfo geo where a.blastid=geo.blastid and geo.delete_flag=0)>0

then 'true' else 'false' means that the qualified blasting amount will be uploaded

end as isShowFlag is the alias of the query statement, and the alias name can be used for subsequent calls.

4.left join left join, table 1 left join table 2, left as the main, indicating that table 1 is the main, associated with the data in table 2, the result of the search shows all the data on the left, and then the data displayed on the rightis the data that intersects with the left.

The meaning of a sentence is to take the intersection first, and then associate it to the left table.

Extended and sorted out the common meanings and distinctions of several connections, as shown in the following table:

5. Query statement select xxxx from table name where query condition

Where the query condition is followed by all the content you want to query, connect with and, here you need to pay attention to the use of order by

order by 1, 2, 3, 4, sort 1 first, if 1 is the same, sort by 2, 3, 4

6. cast () data type conversion function, in the text cast(a.charge_approve as numeric) means to convert the field charge_approve to numeric type, which used to be character type, and character type fields cannot be sorted

7. a.exe_plan_id = b.exe_plan_id means that the exe_plan_id field of table a and the exe_plan_id field of table b are bound. It can be understood that only after the two tables are bound, related query operations can be performed.

Summary of common templates:

Select field name 1, field name 2 case when condition then execute statement else execute statement end as alias from table name alias left join on table join (a.exe_plan_id = b.exe_plan_id)

Where query condition (d.app_time DESC)

Second, how to associate with sql in the development code

There is a word 'mapper mapping' in the development logic, and the specific implementation in it will not be repeated too much.

The simple logic is:

Use the xml file to map the name of the sql statement and the entity name one by one, bind in this form, and then reference the mapped file name in the code to realize data query.

Above we listed the common syntax of mysql through a sql statement, and how to use it in the code after the sql statement is written.

Last:

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