KB to show an example of using EXCHANGE command to switch tables

knowledgebase/exchangeStatementToSwitchTables.md

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+---
+title: How to use the exchange command to switch tables
+description: “How to use the exchange command to switch tables“
+date: 2024-11-21
+---
+
+# How to use the exchange command to switch tables
+
+### Question
+
+How do I use the EXCHANGE command to switch table names?
+
+### Answer
+
+The `EXCHANGE` command is useful when you need to switch a current table with another table that is temporary where possibly Primary Keys or other settings were updated.
+This happens atomically vs with the `RENAME` command.
+It is also useful when you have Materialized Views triggering on a source table and are trying to avoid rebuilding the view.
+
+Below is a simple example on how it works and how to test:
+- Create sample database
+```
+create database db1;
+```
+- Create example table
+```
+create table db1.table1_exchange
+(
+ id Int32,
+ string_field String
+)
+engine = MergeTree()
+order by id;
+```
+- Insert sample row
+```
+insert into db1.table1_exchange
+values
+(1, 'a');
+```
+- Create example temporary table that will be exchanged
+```
+create table db1.table1_exchange_temp
+(
+ id Int32,
+ string_field String
+)
+engine = MergeTree()
+order by id;
+```
+- Insert sample row into the temporary table
+```
+insert into db1.table1_exchange_temp
+values
+(2, 'b');
+```
+- Run the `EXCHANGE` command to switch the tables
+```
+exchange tables db1.table1_exchange and db1.table1_exchange_temp;
+```
+- Test that the tables are now exchanged and show the rows are switched
+```
+clickhouse-cloud :) select * from db1.table1_exchange;
+
+SELECT *
+FROM db1.table1_exchange
+
+Query id: 925a9a54-ce0d-406f-9943-16930f770a65
+
+┌─id─┬─string_field─┐
+│  2 │ b            │
+└────┴──────────────┘
+
+1 row in set. Elapsed: 0.002 sec. 
+```
+Reference link:  
+https://clickhouse.com/docs/en/sql-reference/statements/exchange