SELECT Statement
The SELECT statement can be executed to retrieve data from a table or view. The result is stored in a result table, which is called a result set.
Serving as an overlaid filter for a database table, the SELECT statement filters required data from the table using SQL keywords.
Syntax
SELECT
{ * | [column, ...] }
[ FROM from_item [, ...] ];
Parameter Description
SELECT list
Specifies the name of a column in the table to be queried. The value can be a part of the column name or all of the column names. The wildcard (*) is used to represent all column names.
Column names can be expressed in the following formats:
- Manually input column names which are separated by commas (,)
- Columns computed in the FROM clause
FROM clause
Specifies one or more source tables for the SELECT statement. The FROM clause involves multiple elements. The common elements are as follows:
table_name
Specifies the name of a table or view. The schema name can be added before the table name or view name, for example, schema_name.table_name. The table name is the most common element.
subquery
Performs a subquery in the FROM clause. A temporary table is created to save subquery results. For details, see Subqueries.
alias
Gives a temporary alias to a table to facilitate the reference by other queries. For details, see Aliases.
join_type
There are five types. For details, see JOIN.
Examples
Read all data from the customer_t1 table.
openGauss=# SELECT * FROM customer_t1; c_customer_sk | c_customer_id | c_first_name | c_last_name | amount ---------------+---------------+--------------+-------------+-------- 3869 | hello | Grace | | 1000 3869 | hello | Grace | | 1000 3869 | | Grace | | 3869 | hello | | | 3869 | hello | | | | | | | 6985 | maps | Joes | | 2200 9976 | world | James | | 5000 4421 | Admin | Local | | 3000 (9 rows)
Read the c_customer_sk and c_customer_id columns from the customer_t1 table.
openGauss=# SELECT c_customer_sk,c_customer_id FROM customer_t1; c_customer_sk | c_customer_id ---------------+--------------- 3869 | hello 3869 | hello 3869 | 3869 | hello 3869 | hello | 6985 | maps 9976 | world 4421 | Admin (9 rows)