Here are seven ways to return duplicate rows in MariaDB when those rows have a primary key or other unique identifier column.
Therefore, the duplicate rows share exactly the same values across all columns except for their unique identifier column.
MariaDB
Fix “ERROR 1222 (21000): The used SELECT statements have a different number of columns” when using UNION in MariaDB
When using the UNION operator in MariaDB, you may encounter the following error: “ERROR 1222 (21000): The used SELECT statements have a different number of columns”.
This error occurs when the number of columns returned by each SELECT statement is different.
The way to fix this is to ensure that both SELECT statements return the same number of columns.
2 Ways to Delete Duplicate Rows in MariaDB (Ignores Primary Key)
Here are examples of removing duplicate rows from a table in MariaDB when those rows have a primary key or unique identifier column.
The examples delete duplicate rows but keep one. So in the case of two identical rows, it deletes one of them and keeps the other.
4 Ways to List All Tables in a MariaDB Database
Below are four ways to list out the tables in a MariaDB database using SQL or the command line.
4 Ways to Select Duplicate Rows in MariaDB
If you have a table that you suspect has duplicate rows in your MariaDB database, you can use any of the following queries to get an idea of how many rows are duplicates.
Fix “ERROR 1054 (42S22): Unknown column ‘…’ in ‘on clause'” in MariaDB
If you’re getting an error that reads something like “ERROR 1054 (42S22): Unknown column ‘tab.ColName’ in ‘on clause”” in MariaDB, here are three likely causes:
- The column doesn’t exist.
- You’re trying to reference an aliased column by its column name.
- Or it could be the other way around. You could be referencing the column with an alias that was never declared.
Fix “ERROR 1250 (42000): Table ‘…’ from one of the SELECTs cannot be used in ORDER clause” in MariaDB
If you’re getting “ERROR 1250 (42000): Table ‘…’ from one of the SELECTs cannot be used in ORDER clause”, it’s probably because you’re qualifying a column name with its table name when using an operator such as UNION, INTERSECT, or EXCEPT in MariaDB.
To fix this, either remove the table name or use a column alias.
Fix “ERROR 1054 (42S22): Unknown column ‘colname’ in ‘order clause'” in MariaDB
If you’re getting error “ERROR 1054 (42S22): Unknown column ‘colname’ in ‘order clause’” in MariaDB, it may be that you’re trying to reference an aliased column by its column name.
This is a common error when running queries that join two or more tables. It can also happen when using operators such as UNION, INTERSECT, and EXCEPT.
2 Ways to Return Rows that Contain Only Alphanumeric Characters in MariaDB
Below are two methods for returning rows that only contain alphanumeric characters in MariaDB.
Alphanumeric characters are alphabetic characters and numeric characters.