The [where] argument

This page is part of the magic.data.common documentation.

This argument is common for [sql.update], [sql.delete], and [sql.read], in addition to that a [join] will also be logically parsed much the same way as a [where] argument. The where argument follows a recursive structure, allowing you to supply multiple layers of where criteria, being applied recursively, using some sort of comparison operator, applied to all conditions in the same level. Its most basic usage is as follows.

sql.read
   table:table1
   limit:-1
   where

      and
         field1:howdy

The above would result in the following result.

sql.read:select * from 'table1' where 'field1' = @0
   @0:howdy

To apply multiple [and] criteria, you can simply add them consecutively as follows.

sql.read
   table:table1
   limit:-1
   where

      and
         field1:howdy
         field2:world

The above results in the following.

sql.read:select * from 'table1' where 'field1' = @0 and 'field2' = @1
   @0:howdy
   @1:world

If you exchange the above [and] with [or], the system will use the or operator to separate your arguments, such as the following illustrates.

sql.read
   table:table1
   limit:-1
   where

      or
         field1:howdy
         field2:world

The above results in the following result.

sql.read:select * from 'table1' where 'field1' = @0 or 'field2' = @1
    @0:howdy
    @1:world

You can also nest operators, producing parenthesis, and create complex conditions, such as the following illustrates.

sql.read
   table:table1
   limit:-1
   where

      or
         field1:howdy

         and
            field2:world
            field3:dudes

Which results in the following.

sql.read:select * from 'table1' where 'field1' = @0 or ('field2' = @1 and 'field3' = @2)
   @0:howdy
   @1:world
   @2:dudes

The parent of a list of criteria is deciding which logical operator to separate your conditions with, contrary to traditional languages, where you separate your conditions with the logical operator, and explicitly add parenthesis to group your levels. This might seem a little bit weird in the beginning, but this is a general rule with everything in Hyperlambda, and after a while will feel more natural than the alternative. The reasons for this is to allow for semantically traversing your lambda objects, allowing the computer to logically understand what it does more easily - Among other things. Think of the boolean logical parts of your SQL slots as “grouping your comparisons” or a “logical function invocation” if it helps.

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