ClickHouse/docs/en/sql-reference/statements/create/row-policy.md

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41	ROW POLICY

CREATE ROW POLICY

Creates a row policy, i.e. a filter used to determine which rows a user can read from a table.

:::warning
Row policies makes sense only for users with readonly access. If user can modify table or copy partitions between tables, it defeats the restrictions of row policies. :::

Syntax:

CREATE [ROW] POLICY [IF NOT EXISTS | OR REPLACE] policy_name1 [ON CLUSTER cluster_name1] ON [db1.]table1
        [, policy_name2 [ON CLUSTER cluster_name2] ON [db2.]table2 ...]
    [FOR SELECT] USING condition
    [AS {PERMISSIVE | RESTRICTIVE}]
    [TO {role1 [, role2 ...] | ALL | ALL EXCEPT role1 [, role2 ...]}]

USING Clause

Allows to specify a condition to filter rows. An user will see a row if the condition is calculated to non-zero for the row.

TO Clause

In the section TO you can provide a list of users and roles this policy should work for. For example, CREATE ROW POLICY ... TO accountant, john@localhost.

Keyword ALL means all the ClickHouse users including current user. Keyword ALL EXCEPT allow to exclude some users from the all users list, for example, CREATE ROW POLICY ... TO ALL EXCEPT accountant, john@localhost

:::note
If there are no row policies defined for a table then any user can SELECT all the row from the table. Defining one or more row policies for the table makes the access to the table depending on the row policies no matter if those row policies are defined for the current user or not. For example, the following policy

CREATE ROW POLICY pol1 ON mydb.table1 USING b=1 TO mira, peter

forbids the users mira and peter to see the rows with b != 1, and any non-mentioned user (e.g., the user paul) will see no rows from mydb.table1 at all.

If that's not desirable it can't be fixed by adding one more row policy, like the following:

CREATE ROW POLICY pol2 ON mydb.table1 USING 1 TO ALL EXCEPT mira, peter :::

AS Clause

It's allowed to have more than one policy enabled on the same table for the same user at the one time. So we need a way to combine the conditions from multiple policies.

By default policies are combined using the boolean OR operator. For example, the following policies

CREATE ROW POLICY pol1 ON mydb.table1 USING b=1 TO mira, peter
CREATE ROW POLICY pol2 ON mydb.table1 USING c=2 TO peter, antonio

enables the user peter to see rows with either b=1 or c=2.

The AS clause specifies how policies should be combined with other policies. Policies can be either permissive or restrictive. By default policies are permissive, which means they are combined using the boolean OR operator.

A policy can be defined as restrictive as an alternative. Restrictive policies are combined using the boolean AND operator.

Here is the general formula:

row_is_visible = (one or more of the permissive policies' conditions are non-zero) AND
                 (all of the restrictive policies's conditions are non-zero)

For example, the following policies

CREATE ROW POLICY pol1 ON mydb.table1 USING b=1 TO mira, peter
CREATE ROW POLICY pol2 ON mydb.table1 USING c=2 AS RESTRICTIVE TO peter, antonio

enables the user peter to see rows only if both b=1 AND c=2.

ON CLUSTER Clause

Allows creating row policies on a cluster, see Distributed DDL.

Examples

CREATE ROW POLICY filter1 ON mydb.mytable USING a<1000 TO accountant, john@localhost

CREATE ROW POLICY filter2 ON mydb.mytable USING a<1000 AND b=5 TO ALL EXCEPT mira

CREATE ROW POLICY filter3 ON mydb.mytable USING 1 TO admin