Error in compiling SQL Expression

Question

In the [Error in SQL Expression; thread, Kurt Reinhardt wrote "Please note, a SQL Expression can only return a single, distinct value per each record in the main recordset.", I tried this where my main Record Selection's SQL query is:
{GLF_LDG_ACC_TRANS.ldg_name} = {@&CH_LDG_GL_ACT_CURR} and
{GLF_LDG_ACC_TRANS.period} = {@&CH_PERIOD_GL_CURR} and
{GLF_LDG_ACC_TRANS.ACCNBRI}  "99991103" and
{GLF_LDG_ACC_TRANS.DOC_REF1}  "{%SundryCreditors}" and
{GLF_LDG_ACC_TRANS.DOC_TYPE} = "$APINVCE"
My SQL Expression %SundryCreditors is:
select doc_ref1
from glf_ldg_acc_trans
where ldg_name = 'APLED09'
  and period = "GLF_LDG_ACC_TRANS"."PERIOD"
  and doc_ref1 = "GLF_LDG_ACC_TRANS"."DOC_REF1"
  and accnbri like 'SUNDRY%'
which essentially queries the same table as the main recordset using the same key fields, and returns one row only. However, when I click on the Check button in the Formula Workshop window, I get the error message "Error in compiling SQL Expression : Database Connection Error: '42000:MicrosoftODBC SQL Server DriverSQL ServerIncorrect syntax near the keyword 'select'. Database Vendor Code: 156 '".
Do you know what is my issue?

Answer 1

If you know what you're doing, you can add a full select statement into a SQL Expression... And Kurt is correct when he says that it may only return a single row of info. Don is also correct when he says that this not what SQL commands are designed for.
Here's what's happening...
When you link your tables in the Database Expert and drop fields onto the design surface (and optionally, add criteria to the Select Expert), CR builds out a SQL statement that can is to be sent out to the db server so that the data can be returned. You can view this SQL by going to Database > Show SQL Query...
When you add a SQL Expression, CR inserts it into the SQL Query as another data column. This is typically done to take advantage of functions that are available in the data base but not in CR.
A few crafty individuals, like Kurt, have figured out that you can in fact inset a full SELECT query into a SQL Expression and it will be inserted into the CR generated querie's SELECT list as a sub-query.
Bear in mind 2 things... #1) You have to be familiar with SQL syntax, namely you have to know the proper syntax for using sub-queries in a SELECT list in your data base. #2) CR doesn't officially support is behavior and they won't offer you any help if the current functionality is removed in later versions.
HTH,
Jason