In SQL, the ALTER TABLE statement modifies the definition of an existing table.
You can use ALTER TABLE to alter, add, or drop columns and constraints.
Depending on your DBMS, the ALTER TABLE statement can also be used to reassign and rebuild partitions, or disable and enable constraints and triggers.
In SQL, the UNION clause concatenates the results of two queries into a single result set.
You can use the UNION clause with or without the ALL argument:
UNION ALL – Includes duplicates.UNION – Excludes duplicates.Some RDBMSs also accept UNION DISTINCT, which is the equivalent to UNION. That is, it excludes duplicates.
Below are some basic examples to demonstrate how it works.
Continue readingIn SQL, the AVG() function is an aggregate function that returns the average of all values in a given expression.
It can also be used to return the average of all distinct (unique) values in an expression.
The expression must be numeric (it cannot be character string, bit string, or datetime).
Below are some basic examples to demonstrate how it works.
Continue readingIn SQL, the SUM() function is an aggregate function that returns the sum of all values in a given expression.
It can also be used to return the sum of all distinct (unique) values in an expression.
The expression must be numeric (it cannot be character string, bit string, or datetime).
Below are some basic examples to demonstrate how it works.
Continue readingIn SQL, the MAX() function is an aggregate function that returns the maximum value in a given expression.
Below are some basic examples to demonstrate how it works.
Continue readingIn SQL, the MIN() function is an aggregate function that returns the minimum value in a given expression.
Below are some basic examples to demonstrate how it works.
Continue readingIn 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).
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