Commonly used basic operation syntax of mysql (4) - simple unconditional query of data and database and table query [command line mode]

1. Mysql simple query: select field 1, field 2... from tablename;

If you write a * in the field, it means querying all The field is equivalent to specifying all field names, so if you want to query the data of all fields, you generally use *.

2. Deduplication query: select distinct field 1, field 2... form tablename;

can be combined with the previous picture To compare the results.

3. Perform the four mathematical operations directly during query, including addition, subtraction, multiplication and division:

##4 , rename the query result fields when querying; select field 1 as name 1, field 2 as name 2... from tablename;

## Use as to rename here. In fact, as can be omitted:

5. Use concat Connect the string to get the query result in a custom format:

6. Suddenly I remembered that there were libraries and tables added before. The deletion operation misses the query operation. Here is the supplement:

Query all databases show databases;

Query all tables under the current database show tables;

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