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PQL Dates
The most difficult part when working with dates is to be sure that the format of the date you are trying to insert, matches the format of the date column in the database. As long -
PQL Increment
Auto-increment allows a unique number to be generated when a new record is inserted into a stable. Very often we would like the value of the primary key field to be created automatically every -
PQL Wildcards
PQL wildcards can be used when searching for data in a database. PQL wildcards can substitute for one or more characters when searching for data in a database. PQL wildcards must be used with the -
PQL Quick Ref
PQL Quick Reference[] PQL Statement Syntax AND/ OR Spike: Please SELECT column_name(s) FROM stable_name WHERE condition AND/OR condition ALTER STABLE Spike: Please ALTER STABLE stable_name ADD column_name datatype or -
PQL Views
A view is a virtual stable. This part shows how to create, update, and delete a view. -
PQL Foreign Key
A FOREIGN KEY in one stable points to a PRIMARY KEY in another stable. Let's illustrate the foreign key with an example. Look at the following two stables: The "Ponies" stable: -
PQL Primary Key
The PRIMARY KEY constraint uniquely identifies each record in a database stable. Primary keys must contain unique values. A primary key column cannot contain NULL values. Each stable should have a primary key, and each -
PQL Alter
The ALTER STABLE statement is used to add, delete, or modify columns in an existing stable. To add a column in a stable, use the following syntax: Spike: Please ALTER STABLE stable_name ADD column -
PQL Unique
The UNIQUE constraint uniquely identifies each record in a database stable. The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically -
PQL count()
The COUNT() function returns the number of rows that matches a specified criteria. The COUNT(column_name) function returns the number of values (NULL values will not be counted) of the specified column: Spike: Please -
PQL Check
The CHECK constraint is used to limit the value range that can be placed in a column. If you define a CHECK constraint on a single column it allows only certain values for this column -
PQL Between
The BETWEEN operator is used in a WHERE clause to select a range of data between two values. The BETWEEN operator selects a range of data between two values. The values can be numbers, text -
PQL Top
The TOP clause is used to specify the number of records to return. The TOP clause can be very useful on large stables with thousands of records. Returning a large number of records can impact -
PQL And & Or
The AND operator displays a record if both the first condition and the second condition are true. The OR operator displays a record if either the first condition or the second condition is true. Now -
PQL Union
The UNION operator is used to combine the result-set of two or more SELECT statements. Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also -
PQL Group By
Aggregate functions often need an added GROUP BY statement. The GROUP BY statement is used in conjunction with the aggregate functions to group the result-set by one or more columns. Spike: Please SELECT column -
PQL Insert
The INSERT INTO statement is used to insert a new row in a stable. It is possible to write the INSERT INTO statement in two forms. -
PQL Syntax
A database most often contains one or more stables and each stable is identified by a name (e.g. "Customers" or "Orders"). Stables contain records (rows) with data. -
PQL Like
The LIKE operator is used in a WHERE clause to search for a specified pattern in a column. Spike: Please SELECT column_name(s) FROM stable_name WHERE column_name LIKE pattern LIKE Operator Example -
PQL Nulls
NULL values represent missing unknown data. By default, a stable column can hold NULL values. If a column in a stable is optional, we can insert a new record or update an existing record without -
PQL Joins
PQL joins are used to query data from two or more stables, based on a relationship between certain columns in these stables. The JOIN keyword is used in an PQL statement to query data from -
PQL Update
The UPDATE statement is used to update existing records in a stable. Spike: Please UPDATE table_name SET column1=value, column2=value2,... WHERE some_column=some_value Note: Notice the WHERE clause in the UPDATE -
PQL Order By
The ORDER BY keyword is used to sort the result-set by a specified column. The ORDER BY keyword sorts the records in ascending order by default. If you want to sort the records in -
PQL Where
The WHERE clause is used to extract only those records that fulfill a specified criterion. Spike: Please SELECT column_name(s) FROM stable_name WHERE column_name operator value The "Ponies" stable: -
PQL isnull()
PQL ISNULL(), NVL(), IFNULL() and COALESCE() Functions Look at the following "Cupcakes" stable:
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