Wavetronix Command Translator (CMD-DT) - User Guide Bedienungsanleitung PDF herunterladen (Seite 152)

APPENDIX 151

TableOne and TableTwo, each contain four columns (the data types of these columns are

usually not necessary to know):

 TableOne – One, Two, ree, Four

 TableTwo – Five, Six, Seven, Eight

A basic SELECT query, which will grab all data rows and columns from TableOne, will look

like this:

SELECT * from TableOne

e “*” character represents a desire to have all columns and all rows from TableOne. is

basic query is usually unnecessary because TaskBuilder operations default to a “select all”

without needing to write a specic SQL statement. If you want all information in TableOne,

the regular TaskBuilder behavior can be used without writing SQL.

Selecting One or More Columns From a Table

If you desire columns One and Four from TableOne, but not Two and ree, then replace

the “*” with the specic column names separated by commas:

SELECT One, Four from TableOne

You can specify an unlimited number of columns in a SELECT statement. If desired, you

can also select columns more than once:

SELECT Two, Three, Four, Two from TableOne

e resulting data set will have four columns with data from column Two being in both the

rst and last columns. is is redundant, but the option is available.

Selecting One or More Data Rows From a Table

Another common operation is selecting only certain rows that meet certain criteria from

the data table. To add a qualier to the query, use a WHERE clause; strings must be en-

closed in single quotation marks:

SELECT * from TableOne WHERE One > 100

SELECT * from TableTwo WHERE Six = ‘Hello’

e data types of each column will need to be known for WHERE statements to be created.

An error will occur in column six if the WHERE Six = ‘Hello’ statement contains integers.

e query will return an empty set if the data row does not meet the criteria.

Multiple WHERE clauses can be used by conjoining them with either the AND or OR

keywords:

1 2 ... 147 148 149 150 151 152 153 154 155 156

Keine Kommentare

Wavetronix Command Translator (CMD-DT) - User Guide Bedienungsanleitung Seite 152