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GetSQLValueFromSource

function GetSQLValueFromSource(const aSQL: string;
  aDBIndex: integer): variant;

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := GetSQLValueFromSource(
    'select count(*) from ExampleInbound where ReadFlag = 0', 0);
end;

Usage​

GetSQLValueFromSource runs a query on a selected source connection and returns the first field value or Null.

Parameters

NameTypeDescription
aSQLstring, constCursor query whose first column contains the wanted value. Parameter recognition is disabled.
aDBIndexintegerZero-based source connection index.

Returns

The first cell on success; otherwise the initialised Null for errors caught after query creation. SQL NULL and an empty cursor's first-field value normally also produce Null, so absence, a caught error and a legitimate null cannot be distinguished from the value alone. Index/query-creation failures occur before the handler and can propagate.

Security and safety

Do not concatenate untrusted data or log secrets. Shape and bound the query so the database can return a scalar efficiently. The synchronous external call and mutable active-map connection are not suitable for concurrent reuse.

Additional Technical Info​

GetSQLValueFromSource opens query SQL on a selected source connection and returns the first field's Variant value from the current first row.

The table is fictional. The example is source-reviewed and was not executed.

Implementation

The method creates a temporary query from FSource.DBCons[aDBIndex].DBCon.SQLDATA, disables parameter checking, adds/logs SQL, opens it, reads Fields[0].Value, closes it and frees it. It performs no explicit transaction operation. A local TField variable is declared but never used; this does not change behaviour.

It does not verify record or field counts, call First, or reject multiple rows/columns. On an empty cursor, a Delphi field getter normally returns Null; if the result has no field at index 0, access raises and is logged inside the inner handler. As in the destination variant, failures while evaluating the indexed NewQuery expression occur before both try blocks and propagate rather than reduce to Null.

Side effects and errors

The exact SQL is logged. Query-body errors are logged with script and SQL context and suppressed. The temporary cursor is freed. Source connection/autocommit state is inherited rather than managed here.

Related entries

External references

Created 2026-07-15