ReadVitamin

Like many other Structured Query Languages, to a very large extent, Teradata SQL is also ANSI compatible and also there are extensions available for the same. Let’s start with some basic operators we use in our day to day query building.

As you know the SELECT statement returns all the rows of a table and it might take a long time in case the table is huge. So we use the ‘WHERE’ clause to limit the output and also to run the query fast. When you want to you use the ‘WHERE’ clause you would need comparison operators to compare the column value with another column value or constant value. Point to note here is, while using the ‘WHERE’ clause, the first positional parameter after the keyword ‘WHERE’ has to be a column name and you can not use a constant. Here is the syntax

SELECT {*|<Col1>}, <Col2>, <Col3>…

FROM <table name>

WHERE <column name> <operator> <another column name or constant value>

Following are the comparison operators present in Teradata environment.

For Equal To	For NOT Equal to	For Less Than	For Greater Than	Less Than Equal To	Greater Than Equal To
=	<>	<	>	<=	>=

As mentioned, there are also Teradata Extensions available for the above operators as follows

For Equal To	For NOT Equal to	For Less Than	For Greater Than	Less Than Equal To	Greater Than Equal To
EQ	NE	LT	GT	LE	GE

One can also use logical operators such as AND, OR to the above comparison operators in case there is a need to check multiple conditions. The syntax is;

SELECT {*|<Col1>}, <Col2>, <Col3>…

FROM <table name>

WHERE <column name> <operator> <another column name or constant value>

{AND | OR} <column name> <operator> <another column name or constant value>

In case of logical operators when you are going to use both of them ‘AND’ and ‘OR’ on a single SELECT statement (especially OR before AND), you might be aware that AND is evaluated first. To make sure you evaluate OR first, put the OR condition in braces.

Popularity: 21% [?]