SELECT
Every SQL query will begin with the SELECT
command to fetch data from one or more tables.
Syntax
The SELECT
command is followed by one or more column names to be returned from the table(s) listed in the FROM
clause:
SELECT column1, column2, ... columnN FROM table;
SELECT
can also use the special *
character to represent all columns from the table(s):
SELECT * FROM table;
Note: It is best practice to not rely on column order when using *
.
Examples
The following example selects all columns from table1
and table2
with an INNER JOIN
, restricting the rows to where table1.columnA
and table2.columnB
are equal:
SELECT * FROM table1 INNER JOIN table2 ON table1.columnA = table2.columnB;
When selecting all columns from across multiple tables, duplicate column names will generate an error unless they are distinguished with an alias.
The next example selects all columns from table1
and a named column, columnA
, from table2
. It is presumed that both tables have a column named columnA
and, therefore, an alias should be used to avoid an error:
SELECT table1.*, table2.columnA AS colA, table2.columnB FROM table1 INNER JOIN table2 ON table1.columnA = table2.columnB;
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