shsql: null

SQL database system
| Manual page for null(TDH)

## NULL handling

In shsql statements and results, `NULL` represents a field that is empty, blank, or has no value.``

## NULL in SQL statements

`NULL` may be specified in upper or lower case.``

In where clauses, it may appear on the right-hand side of equality comparisons using any of the constructs shown below:

  `X = null` `X is null`

  `X != null` `X isnot null` `X <> null`

`NULL` may also appear as a member of a list for operations such as `IN`:

  `X in "A,B,C,null"`

## NULL in result rows

shsql(1) represents `NULL` fields as `null` by default.`` When using the API, `NULL` fields are represented in returned result rows using the internal code discussed below, which is equals-sign (=) by default. The calling program can convert these fields as desired.``

## Internal representation of NULL

In data files `NULL` is stored using a certain code.`` By default this code is a single equals sign (`=`), but this can be set in your project config file to be any symbol up to 4 characters in length.`` Your `NULL` symbol should not cooincide with something that could occur as a meaningful non-null field in your data.``

A data record containing three null fields, using the default null symbol, would look like this in the data table file:

  `28 Phoenix = = =`
  Copyright Steve Grubb

Markup created by unroff 1.0, `` `` March 18, 2004.