In SQL, the COUNT() function is an aggregate function that returns the number of items found in a group.
You can use COUNT() in multiple parts of a query. For example, you can use it in the SELECT list, or the HAVING clause when filtering groups.
In SQL, the HAVING clause can be used to specify a search condition for a group or an aggregate.
The HAVING clause is typically used with the GROUP BY clause. In cases where it’s not, there is an implicit single, aggregated group.
The SELECT statement is almost without doubt, the most commonly used statement in SQL.
The SELECT statement is used for retrieving data from the database. You can specify which rows you want returned, and which columns.
If you have a partitioned table or index in SQL Server, and you want to determine which partition a given value would be mapped to, you can do this nice and quickly with the $PARTITION system function.
All you need to know is the name of the partition function (and of course, the value you’re interested in).
Continue readingIn SQL, the GROUP BY clause can be used to divide the results of a query into groups of rows.
This is usually done in order to perform one or more aggregations on each group.
Continue readingThe ORDER BY clause is commonly used in SQL to sort the results of a query.
It allows you to specify the order in which the results are returned.
You can specify whether the results are sorted in ascending order or descending order. You can also specify multiple columns for sorting.
Continue readingThere are four transaction modes in SQL Server. One of these is implicit mode.
In SQL Server, an implicit transaction is when a new transaction is implicitly started when the prior transaction completes, but each transaction is explicitly completed with a COMMIT or ROLLBACK statement.
This is not to be confused with autocommit mode, where the transaction is started and ended implicitly.
Continue readingIn SQL, transactions are used to maintain data integrity by ensuring that a sequence of SQL statements execute completely or not at all.
Transactions manage sequences of SQL statements that must be executed as a single unit of work, so that the database never contains the results of partial operations.
When a transaction makes multiple changes to the database, either all the changes succeed when the transaction is committed, or all the changes are undone when the transaction is rolled back.
Continue readingSQL Server error Msg 245, Level 16 tells us that there was a problem when trying to convert a value to a specific data type.
You’ll get this error if you try to insert the wrong data type into a column.
To fix this issue, make sure the data type of the value you’re trying to insert, matches the column’s type.
Continue readingIf you’ve previously created a partitioned table in SQL Server, and you now want to know how many rows are being stored in each partition, here are three queries you can use.
In particular, you can:
sys.dm_db_partition_stats viewsys.partitions view$PARTITION function in a queryBelow are examples of all three.
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