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I'm new to MySQL. Can anyone describe lines below which I get theme from the demo of the jqgrid, what is the meaning of a.id? What is the meaning of these dots?
$SQL = "SELECT a.id, a.invdate, b.name, a.amount,a.tax,a.total,a.note FROM invheader a, clients b WHERE a.client_id=b.client_id ORDER BY $sidx $sord LIMIT $start , $limit";
You can find the example here: http://trirand.com/blog/jqgrid/jqgrid.html in the advanced>Multi select
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Dot notation (sometimes called the membership operator ) qualifies an SQL identifier with another SQL identifier of which it is a component. You separate the identifiers with the period (.) symbol. Column projections qualify a column name with the following SQL identifiers: Table name: table_name .
The two dots indicate that the schema name is not specified. The PUBLIC default schema is always referenced. Note that this notational format is provided mostly for compatibility with other systems, such as Microsoft SQL Server and IBM Netezza. Using this notation in new queries is discouraged.
The asterisk or star symbol ( * ) means all columns. The semi-colon ( ; ) terminates the statement like a period in sentence or question mark in a question.
The SQL LIKE Operator The percent sign (%) represents zero, one, or multiple characters. The underscore sign (_) represents one, single character.
You've asked several questions here. To address the dots:
In the FROM clause, a is used as an alias for the invheader table. This means you can reference that table by the short alias a instead of the full table name.
Therefore, a.id refers the the id column of the invheader table.
It is generally considered bad practice to simply give your tables the aliases a, b, c, etc. and I would recommend you use something more useful.
I suggest you read some basic MySQL tutorials as this is a fundamental principal.
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