jQuery Grid Plugin - jqGrid

Hi when I use this sentence don't show me nothing in my grid  I use this variable == '$codalbarantmp'

// you can provide custom SQL query to display data

$g->select_command = "SELECT * FROM (SELECT i.codalbaran, i.numlinea, c.referencia, c.descripcion, i.cantidad, i.importe FROM pedidoslineatmp i INNER JOIN articulos c  ON i.codigo = c.codarticulo WHERE i.codalbaran = '$codalbarantmp')  o";

// you can provide custom SQL query to display data 

But this sentence is OK works prefect

$g->select_command = "SELECT * FROM (SELECT i.codalbaran, i.numlinea, c.referencia, c.descripcion, i.cantidad, i.importe FROM pedidoslineatmp i INNER JOIN articulos c  ON i.codigo = c.codarticulo WHERE i.codalbaran =11000)  o";