The MySQL REPLACE statement allows us to replace data in a table with new data. The new data can be explicitly provided in the statement or it could come from the result of a query. Therefore, we can use the REPLACE statement to effectively “refresh” a table with new/updated data from another table.
Category: MySQL
Fix “Unknown event” Error in MySQL when Trying to Drop an Event
If you’re getting an error that reads something like “ERROR 1539 (HY000): Unknown event ‘Event1’” in MySQL when trying to drop an event, it’s probably because the event that you’re trying to drop doesn’t exist.
There are a couple of ways to address this issue. One way is to use the IF EXISTS clause so that dropping a non-existent event doesn’t cause an error. Another way is to check the name of the event that you’re trying to drop – it could be that you’re using the wrong event name.
How to Drop a Primary Key in MySQL
In general, once we create a primary key on a table we leave it there. It’s there to help us maintain data integrity and removing it can put that data integrity at risk.
But sometimes we might have good reason to remove a primary key. Perhaps we need to drop it so that we can create a primary key on a different column or multiple columns. Or perhaps there’s another valid reason to drop the primary key.
Either way, below is an example of dropping the primary key from a column.
Continue readingFix “Variable ‘event_scheduler’ is a GLOBAL variable and should be set with SET GLOBAL” in MySQL
If you’re getting an error that reads “ERROR 1229 (HY000): Variable ‘event_scheduler’ is a GLOBAL variable and should be set with SET GLOBAL” in MySQL, it’s probably because you’re trying to set the event_scheduler system variable, but you’re not specifying it as a global variable.
The event_scheduler variable is a global variable and so we must specify it as a global variable.
To fix this issue, specify it as a global variable when setting it’s value.
Continue readingHow to Hide a GIPK from the SHOW CREATE TABLE Statement (and SHOW COLUMNS and SHOW INDEX) in MySQL
When we have a table with a generated invisible primary key (GIPK) in MySQL, we can usually see its definition when we use various SHOW statements such as SHOW CREATE TABLE, SHOW COLUMNS, and SHOW INDEX, as well as when we query information schema tables such as information_schema.columns.
But there is a way of hiding the GIPK from such statements. It all comes down to the show_gipk_in_create_table_and_information_schema variable. Yes, there’s actually a system variable that allows us to hide GIPKs from the output of various SHOW statements and information schema tables.
A Quick Intro to SHOW BINARY LOGS in MySQL
In MySQL we can use the SHOW BINARY LOGS statement to return a list of binary log files on the server.
Check Whether GIPKs are Enabled in MySQL
In MySQL, GIPK stands for generated invisible primary key. These are created whenever we create an InnoDB table without explicitly defining primary key.
However, MySQL will only create a GIPK if we have enabled GIPKs. More specifically, a GIPK will only be created when our sql_generate_invisible_primary_key server system variable is set to ON. By default this is set to OFF.
An Overview of SHOW COLLATION in MySQL
In MySQL we can use the SHOW COLLATION statement to return all collations supported by the server. By default it returns all available collations, but we can filter the output down to just those collations that we’re interested in.
Using REPLACE with the TABLE Statement in MySQL
When using the MySQL REPLACE statement to update another table based on a source table, we have the option of using a SELECT statement to select the whole table (or part of it) or the TABLE statement to select the whole table.
Below is an example of refreshing a table from another one using the TABLE statement with the REPLACE statement.
An Overview of the SHOW CHARACTER SET Statement in MySQL
In MySQL we can use the SHOW CHARACTER SET statement to return all available character sets. We can also use it to narrow the output down to just those we’re interested in.