Как удалить запись в таблице postgresql
Для удаления данных в PostgreSQL применяется команда DELETE . Она имеет следующий синтаксис:
Например, удалим строки, у которых производитель — Apple:
Или удалим все товары, производителем которых является HTC и которые имеют цену меньше 35000:
Если необходимо вовсе удалить все строки вне зависимости от условия, то условие можно не указывать:
Как удалить запись в таблице postgresql
DELETE deletes rows that satisfy the WHERE clause from the specified table. If the WHERE clause is absent, the effect is to delete all rows in the table. The result is a valid, but empty table.
TRUNCATE provides a faster mechanism to remove all rows from a table.
There are two ways to delete rows in a table using information contained in other tables in the database: using sub-selects, or specifying additional tables in the USING clause. Which technique is more appropriate depends on the specific circumstances.
The optional RETURNING clause causes DELETE to compute and return value(s) based on each row actually deleted. Any expression using the table’s columns, and/or columns of other tables mentioned in USING , can be computed. The syntax of the RETURNING list is identical to that of the output list of SELECT .
You must have the DELETE privilege on the table to delete from it, as well as the SELECT privilege for any table in the USING clause or whose values are read in the condition .
The WITH clause allows you to specify one or more subqueries that can be referenced by name in the DELETE query. See Section 7.8 and SELECT for details. table_name
The name (optionally schema-qualified) of the table to delete rows from. If ONLY is specified before the table name, matching rows are deleted from the named table only. If ONLY is not specified, matching rows are also deleted from any tables inheriting from the named table. Optionally, * can be specified after the table name to explicitly indicate that descendant tables are included. alias
A substitute name for the target table. When an alias is provided, it completely hides the actual name of the table. For example, given DELETE FROM foo AS f , the remainder of the DELETE statement must refer to this table as f not foo . from_item
A table expression allowing columns from other tables to appear in the WHERE condition. This uses the same syntax as the FROM clause of a SELECT statement; for example, an alias for the table name can be specified. Do not repeat the target table as a from_item unless you wish to set up a self-join (in which case it must appear with an alias in the from_item ). condition
An expression that returns a value of type boolean . Only rows for which this expression returns true will be deleted. cursor_name
The name of the cursor to use in a WHERE CURRENT OF condition. The row to be deleted is the one most recently fetched from this cursor. The cursor must be a non-grouping query on the DELETE ‘s target table. Note that WHERE CURRENT OF cannot be specified together with a Boolean condition. See DECLARE for more information about using cursors with WHERE CURRENT OF . output_expression
An expression to be computed and returned by the DELETE command after each row is deleted. The expression can use any column names of the table named by table_name or table(s) listed in USING . Write * to return all columns. output_name
A name to use for a returned column.
On successful completion, a DELETE command returns a command tag of the form
The count is the number of rows deleted. Note that the number may be less than the number of rows that matched the condition when deletes were suppressed by a BEFORE DELETE trigger. If count is 0, no rows were deleted by the query (this is not considered an error).
If the DELETE command contains a RETURNING clause, the result will be similar to that of a SELECT statement containing the columns and values defined in the RETURNING list, computed over the row(s) deleted by the command.
PostgreSQL lets you reference columns of other tables in the WHERE condition by specifying the other tables in the USING clause. For example, to delete all films produced by a given producer, one can do:
What is essentially happening here is a join between films and producers , with all successfully joined films rows being marked for deletion. This syntax is not standard. A more standard way to do it is:
In some cases the join style is easier to write or faster to execute than the sub-select style.
Delete all films but musicals:
Clear the table films :
Delete completed tasks, returning full details of the deleted rows:
Delete the row of tasks on which the cursor c_tasks is currently positioned:
Summary: in this tutorial, you will learn how to use the PostgreSQL DELETE statement to delete data from a table.
Introduction to PostgreSQL DELETE statement
The PostgreSQL DELETE statement allows you to delete one or more rows from a table.
The following shows basic syntax of the DELETE statement:
- First, specify the name of the table from which you want to delete data after the DELETE FROM keywords.
- Second, use a condition in the WHERE clause to specify which rows from the table to delete.
The WHERE clause is optional. If you omit the WHERE clause, the DELETE statement will delete all rows in the table.
The DELETE statement returns the number of rows deleted. It returns zero if the DELETE statement did not delete any row.
To return the deleted row(s) to the client, you use the RETURNING clause as follows:
The asterisk ( * ) allows you to return all columns of the deleted row from the table_name .
To return specific columns, you specify them after the RETURNING keyword.
Note that the DELETE statement only removes data from a table. It doesn’t modify the structure of the table. If you want to change the structure of a table such as removing a column, you should use the ALTER TABLE statement.
PostgreSQL DELETE statement examples
Let’s set up a sample table for the demonstration.
The following statements create a new table called links and insert some sample data:
Here are the contents of the links table:
1) Using PostgreSQL DELETE to delete one row from the table
The following statement uses the DELETE statement to delete one row with the id 8 from the links table:
The statement returns 1 indicated that one row has been deleted:
The following statement uses the DELETE statement to delete the row with id 10:
Since the row with id 10 does not exist, the statement returns 0:
2) Using PostgreSQL DELETE to delete a row and return the deleted row
The following statement deletes the row with id 7 and returns the deleted row to the client:
PostgreSQL returns the following deleted row:
3) Using PostgreSQL DELETE to delete multiple rows from the table
The following statement deletes two rows from the links table and return the values in the id column of deleted rows:
4) Using PostgreSQL DELETE to delete all rows from the table
The following statement uses the DELETE statement without a WHERE clause to delete all rows from the links table:
PostgreSQL delete all content
Hello I want to delete all data in my postgresql tables, but not the table itself. How could I do this?
4 Answers 4
The content of the table/tables in PostgreSQL database can be deleted in several ways.
Deleting table content using sql:
Deleting content of one table:
Deleting content of all named tables:
Deleting content of named tables and tables that reference to them (I will explain it in more details later in this answer):
Deleting table content using pgAdmin:
Deleting content of one table:
Deleting content of table and tables that reference to it:
Difference between delete and truncate:
From the documentation:
DELETE deletes rows that satisfy the WHERE clause from the specified table. If the WHERE clause is absent, the effect is to delete all rows in the table. http://www.postgresql.org/docs/9.3/static/sql-delete.html
TRUNCATE is a PostgreSQL extension that provides a faster mechanism to remove all rows from a table. TRUNCATE quickly removes all rows from a set of tables. It has the same effect as an unqualified DELETE on each table, but since it does not actually scan the tables it is faster. Furthermore, it reclaims disk space immediately, rather than requiring a subsequent VACUUM operation. This is most useful on large tables. http://www.postgresql.org/docs/9.1/static/sql-truncate.html
Working with table that is referenced from other table:
When you have database that has more than one table the tables have probably relationship. As an example there are three tables:
And some prepared data for these tables:
Table orders references table customers and table loyalty_cards references table customers. When you try to TRUNCATE / DELETE FROM the table that is referenced by other table/s (the other table/s has foreign key constraint to the named table) you get an error. To delete content from all three tables you have to name all these tables (the order is not important)
or just the table that is referenced with CASCADE key word (you can name more tables than just one)
The same applies for pgAdmin. Right click on customers table and choose Truncate Cascaded.