If you’re getting the error “ORA-01790: expression must have same datatype as corresponding expression” in Oracle Database, it’s probably because you’re using an operator such as UNION, INTERSECT, or EXCEPT to run a compound query, but the columns returned by each query use different data type groups.
To fix this issue, you’ll need to ensure that each column returned by the second query uses the same data type group as the corresponding column in the first query.
Continue readingHere are five options for using SQL to return only those rows that have the minimum value within their group.
These examples work in most major RDBMSs, including MySQL, MariaDB, Oracle, PostgreSQL, SQLite, and SQL Server.
Continue readingThere are at least a few possible reasons you might be getting the dreaded error 1064 (42000) that reads “You have an error in your SQL syntax…” etc when trying to use the MINUS operator in MariaDB.
I’ll explore these below and offer some solutions.
Continue readingHere are three examples of using SQL to find and select the row with the minimum value in a given column.
The examples work in most major RDBMSs, including MySQL, MariaDB, PostgreSQL, SQLite, Oracle, and SQL Server.
Continue readingThe following examples return duplicate rows from an Oracle Database table.
Continue readingIf you’re getting “ERROR: missing FROM-clause entry for table” in PostgreSQL when using an operator such as UNION, INTERSECT, or EXCEPT, it could be because you’re qualifying a column name with its table name.
To fix this, either remove the table name or use a column alias.
Continue readingHere are four options for returning rows that contain uppercase characters in Oracle Database.
Continue readingWhen using the UNION operator in PostgreSQL, if you encounter an error that reads “ERROR: each UNION query must have the same number of columns“, it’s because there’s a mismatch in the number of columns returned by the queries on either side of the UNION operator.
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.
Below are two methods for returning rows that only contain non-alphanumeric characters in Oracle Database.
Alphanumeric characters are alphabetic characters and numeric characters.
Continue readingHere are seven options for finding duplicate rows in SQL Server, when those rows have a primary key or other unique identifier column.
In other words, the table contains two or more rows that share exactly the same values across all columns except for its unique identifier column.
Continue reading