MongoDB: Function substring - starting index and number of arguments -------------------------------------------------------------------- Key: TEIID-2988 URL: https://issues.jboss.org/browse/TEIID-2988 Project: Teiid Issue Type: Bug Components: Misc. Connectors Affects Versions: 8.4.1 Reporter: Filip Elias Assignee: Ramesh Reddy Labels: Beta1 Fix For: 8.8, 8.7.1, 8.10 Two minor bugs in function substring() Mongo's function $substr takes only 3 arguments so this query fails: {code} SELECT intkey, SUBSTRING(BQT1.SmallA.stringkey, 1) FROM BQT1.SmallA ORDER BY intkey {code} {code} Exception:13:18:48,220 ERROR [org.teiid.CONNECTOR] (Worker38_QueryProcessorQueue345) Connector worker process failed for atomic-request=omsmHP0o16Sa.40.0.86: com.mongodb.CommandFailureException: { "serverUsed" : "localhost/127.0.0.1:27017" , "errmsg" : "exception: the $substr operator requires 3 operand(s)" , "code" : 16020 , "ok" : 0.0} at com.mongodb.CommandResult.getException(CommandResult.java:71) at com.mongodb.CommandResult.throwOnError(CommandResult.java:110) at com.mongodb.DBCollection.aggregate(DBCollection.java:1308) {code} Generated mongo command: {code} { aggregate: "smalla", pipeline: [ { $project: { c_0: "$INTKEY", c_1: { $substr: [ "$STRINGKEY", 1 ] } } }, { $sort: { c_0: 1 } } ] } {code} Mongo's $substr function second argument represents number of bytes to skip, not the starting index. The function substring(StringKey,1,1) returns the second letter, but it should return the first letter.