SQL must know and know

Summary

This book deals with the sorting of data 、 Filtering and grouping , And the watch 、 View 、 coupling 、 Subquery 、 The cursor 、 Stored procedures and triggers .

The first 1 course understand SQL

1.1 Database foundation

1.1.1 database

database （database）
A collection of data stored in some organized way .

1.1.2 surface

surface （table）
A structured list of certain types of data .

Pattern （schema）
Information about the layout and properties of databases and tables .

1.1.3 Columns and data types

Column （column）
A field in the table . All tables are made up of one or more columns .

Decomposing data ——
You can decide how much to break down the data according to your specific needs .

data type （datatype）
Each table column has its own data type , Its restriction （ Or allow ） Data stored in this column .

1.1.4 That's ok

That's ok （row）
A record in a table .

1.1.5 Primary key

Primary key （primary key）
A column of （ Or a set of columns ）, Its value uniquely identifies each row in the table .