If you’re getting an error that reads something like “The correlation name ‘a’ is specified multiple times in a FROM clause’” in SQL Server, it could be that you’re doing a join on two tables, but you’re assigning them the same aliases.
Each table’s alias must be unique.
To fix this issue, be sure to use unique table aliases in your query.
PostgreSQL provides us with a few functions that we can use to convert strings between uppercase and lowercase.
We can convert the whole string to uppercase or lowercase, or we can convert it to initial caps, where the first letter of each word is uppercase and the rest of the word is lowercase.
If you’re getting an error that reads something like “Cannot create index on view ‘MyView’ because the view is not schema bound” in SQL Server, it sounds like you’re trying to create an index on a view that’s not schema bound.
Indexes can only be created on schema bound views.
To fix this issue, define the view as schema bound before creating the index.
SQL subqueries are like little helpers that fetch data for our main query. They’re super handy when we need to filter our results based on some other data in our database.
Probably the most common placement of a subquery in SQL is in the WHERE clause. Placing a subquery in the WHERE clause allows us to compare a column against a set of rows that match a certain criteria.
Let’s look at three quick examples of subqueries in the WHERE clause.
If you’re getting an error that reads something like “Computed column ‘c3’ in table ‘t1’ cannot be persisted because the column is non-deterministic” in SQL Server, it appears that you’re trying to persist a computed column that’s nondeterministic.
A nondeterministic function or expression returns a different result for the same input. If a column uses such an expression, then it will be nondeterministic. A computed column must be deterministic.
A UNIQUE constraint is a rule that we can apply to one or more columns in a database table to ensure that the values in those columns are unique across all rows.
In SQL Server we have a few options when it comes to creating a UNIQUE constraint. But it’s usually done when we create the table or alter it. That is, we include the constraint code in the CREATE TABLE statement or the ALTER TABLE statement.
We can also create a UNIQUE index, which can be used in place of the previous methods, but can have the same effect.
Let’s check out several ways to create a UNIQUE constraint in SQL Server.
If you’re getting an error that reads something like “Cannot create index on view “demo.dbo.SalesSummary” because it uses the aggregate COUNT. Use COUNT_BIG instead” in SQL Server, it’s because you’re trying to create an index on a view that uses the COUNT() function.
PostgreSQL provides us with various string functions, including some that allow us to trim a given string on both sides or a given side.
Below are four functions that we can use to trim strings in PostgreSQL.
If you’re getting an error that reads something like “Cannot DROP TABLE ‘dbo.t1’ because it is being referenced by object ‘v1’” in SQL Server, it looks like you’re trying to drop a table that’s referenced by a schema-bound object (such as a schema-bound view).
If you’re getting an error that reads something like “Computed column ‘c2’ in table ‘t1’ is not allowed to be used in another computed-column definition” in SQL Server, it appears that you’re trying to create a computed column that uses another computed column.
We can’t use other computed columns in our computed column definitions.