SQL Single Table Query

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SELECT statement Format:

SELECT [all| DISTINCT] < target column expression >[,< target column expression;
From < table name or view name >[,< table name or view name >]...| (SELECT statement)
[as]< aliases >
[WHERE < conditional expressions >]
[GROUP by < column name 1> [having < conditional expression >]]
[ORDER by < column name 2> [asc| DESC]];

A query statement can be divided into three parts:

Select clause: Specify the property columns to display FROM clause: Specifies the Query object (base table or view) WHERE clause: Specify query criteria

GROUP BY clause: Groups the results of the query by the values of the specified columns, which have a tuple of equal values for the column. Aggregate functions are typically scoped in each group. Having phrase: Only groups that meet the specified criteria will be output

ORDER BY clause: Sort the query result table in ascending or descending order of the specified column values

1. SELECT:

The < target column expression for the 1.1 Select clause > can be either an attribute column in a table or an expression

SELECT Sname,2018-sage from Student;

SELECT Sname, ' Year of Birth: ', 2018-sage,LOWER(sdept) from Student;

/* Use aliases */

SELECT Sname NAME, ' Year of Birth: ' Birth, 2018-sage BIRTHDAY, LOWER (sdept) DEPARTMENT from Student;

1.2 Removing duplicate rows from values

Specify DISTINCT keywords to remove duplicate rows from the table. If no distinct keyword is specified, all is the default

SELECT DISTINCT Sno from SC;

Common Query conditions:

Query criteria	Predicate
Comparison	=, <, >=, <=,! =, <>,!>,!<; Not+ The above comparison operators
Determine scope	Between and, not between and
Determining the Collection	In, not in
Character matching	Like, isn't like
Null value	Is null, was NOT NULL
Multiple conditions (logical operations)	And, OR, not

SQL Single Table Query