Latest MySQL advanced SQL statement Encyclopedia

Catalog

introduction

One 、 Common query

1、order by Sort by keyword

1.1 Ascending sort

1.2 null

1.3 combination where Perform conditional filtering and then sort

1.4 Multi field sorting

2、and/or Judge

2.1 and/or And the use of and or

2.2 nesting 、 Many conditions of use

3、distinct Query does not duplicate records

4、GROUP BY Group results

5、limit Limit result entries

6、 Set alias （alias—as）

6.1 Number of records in the query table , Display as alias

6.2 utilize as, Import the queried data into another table

7、 wildcard

introduction

Yes MySQL Database query , In addition to basic queries , Sometimes you need to process the result set of the query . For example, take only 10 Data 、 Sort or group the query results, etc .

One 、 Common query 1、order by Sort by keyword

Use SELECT Statement can transfer the required data from MySQL From the database , If you sort the results of the query , have access to order by Statement to sort statements , And finally return the sorted results to the user . The sorting of this statement can not only be for a certain field , You can also target multiple fields .

grammar ：

select Field 1, Field 2... from Table name order by Field 1, Field 2... asc # Query results are displayed in ascending order ,asc It can be omitted select Field 1, Field 2... from Table name order by Field 1, Field 2,... desc # The query results are displayed in descending order

ASC Is sorted in ascending order , Is the default sort method , namely ASC It can be omitted .SELECT If no specific sorting method is specified in the statement , By default ASC Sort by .DESC It is arranged in descending order . Of course order by You can also use where Clause to further filter the query results .

1.1 Ascending sort select name ,score from report order by score;

1.2 null select name ,score from report order by score desc;

1.3 combination where Perform conditional filtering and then sort select name,score,address from report where address='hangzhou' order by score;

1.4 Multi field sorting

ORDER BY Statements can also use multiple fields to sort , When there are multiple records with the same field in the first sorting , These multiple records are sorted according to the second field ,ORDER BY When followed by multiple fields , The fields are separated by English commas , Priority is in order , but order by The next first parameter is only when the same value appears , The second field makes sense .

select name,score,score2 from report order by score2,score desc;

The experiment done here is Sort in ascending order and then in descending order , You can also sort both descending and ascending , There are not too many examples here .

2、and/or Judge

In large databases , Sometimes querying data requires that the data meet certain characteristics and conditions
AND/OR And / or and shell Use the same method in the script

2.1 and/or And the use of and or select name,score,cardid from report where score>80;

select name,score,cardid from report where score>80 and score<90;select name,score,cardid from report where score<60 or score>90;

2.2 nesting 、 Many conditions of use select name,score,cardid from report where score<60 or (score>70 and score<80);select name,score,cardid from report where score<60 or (score>70 and score<=100) order by score desc;

3、distinct Query does not duplicate records select distinct Field from Table name ﹔ distinct Must be placed at the beginning distinct You can only use fields that need to be de duplicated distinct When removing multiple fields , The meaning is ： Only when several fields are repeated at the same time can they be filtered , It will be based on the first field on the left by default .

4、GROUP BY Group results

adopt SQL The result of the search , You can also group them , Use GROUP BY Statement to implement ,GROUP BY Is usually Combining aggregate functions Used together , Common aggregation functions include ： Count （COUNT）、 Sum up （SUM）、 Average （AVG）、 Maximum （MAX）、 minimum value （MIN）,GROUP BY When grouping, the results can be grouped according to one or more fields .

Yes group by The query results of the following fields are summarized and grouped , Usually used in combination with aggregate functions

group by There is a principle , Namely select In all the following columns , Columns that do not use aggregate functions must appear in group by Behind .

select Field , Aggregate functions from Table name (where Field name ( matching ) The number ) group by Field name ;

5、limit Limit result entries

limit Limit the result record of output

In the use of MySQL SELECT Statement to query , The result set returns all matching records （ That's ok ）. Sometimes you just need to return the first line or the first few lines , And that's where it comes in LIMIT Clause .

Grammar format ：select Field from Table name limit [offset,] numberlimit The first parameter is the position offset （ Optional parameters ）, It's settings mysql Which line to start from if the first parameter is not set , It will start from the first record in the table . The first offset is 0, The second is 1offset Subscript for index number Is the number of digits after the index subscript

6、 Set alias （alias—as）

stay mysql When inquiring , When the name of the table is long or some fields in the table are long , To facilitate writing or use the same table multiple times , You can set aliases for fields, columns, or tables , Convenient operation , enhance readability .

Alias of column select Field as Field alias Table name alias of the table select Alias . Field from Table name as Alias as It can be omitted

Use scenarios ：

When querying complex tables , Aliases can shorten the length of query statements when multiple tables are connected （ Easy to understand 、 Shorten sql sentence ）

When setting an alias for a table , Make sure that the alias does not conflict with the names of other tables in the database .

The alias of the column is shown in the result , The alias of the table is not shown in the results , Use... Only when executing queries .

6.1 Number of records in the query table , Display as alias

6.2 utilize as, Import the queried data into another table create table report2 as select * from report;select * from report2;select * from report;

here as What it does ：

Created a new table , And define the table structure , Insert table data （ And school The table is the same ）

however ” constraint “ Not completely ” Copy “ To come over # But if the primary key is set in the original table , Then the attached table ：default The field will be set to one by default 0

7、 wildcard

Wildcards are mainly used to replace some characters in a string , Query the relevant results through the matching of some characters .

Usually, wildcards are used with LIKE Used together , And cooperate with WHERE Clause to complete the query task .

There are two common wildcards , Namely :

%: A percent sign means zero 、 One or more characters _: The underline represents a single character

wildcard “%” and “_” Not only can it be used alone , You can also combine

This is about MySQL senior SQL That's all for the statement article , More about mysql sql Please search the previous articles of software development network or continue to browse the relevant articles below. I hope you will support software development network more in the future ！