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 readingIf 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 readingWhen 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.
In MySQL we can use the SHOW BINARY LOGS statement to return a list of binary log files on the server.
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.
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.
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.
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.
In MySQL we can use the SHOW INDEX statement to return information about the indexes on a table.
We specify which table to show indexes from, and we can optionally specify which database. We can also use a WHERE clause to filter by various criteria.
We can run it against any table where we have some privilege for any column in the table.
Continue readingGenerally speaking, most tables we create in MySQL should have a primary key. A primary key is one or more columns that have been configured as the unique identifier for the table.
We usually create the primary key when creating the table, but we can also add a primary key to an existing table (assuming it doesn’t already have one).
Occasionally it might not be immediately apparent which column is the primary key for a given table. Or it might not be apparent whether or not the table has a composite primary key. Fortunately it’s easy enough to find out.
Below are five ways to get the primary key column/s from an existing table in MySQL.
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