What are the various values and description stored in EXPRTYPE field in PSQRYCRITERIA record?

The Expressions that we create and use in PS-Queries are not saved AS-IS in the back end. They are broken into several parts and stored. A detailed post listing all the tables storing various information on PS-Query's meta data is here - PeopleTools Tables - Part 1 - PeopleTools table for PS-Queries.

A criteria used in a PS-Query gets saved in PSQRYCRITERIA record. A criteria can be between a constant and a field, a field and a subquery, an expression and a constant or simply a field vs another field. When looking at the back end, the EXPRTYPE(Expression Type) which is a numeric field in PSQRYCRITERIA record stores numeric values in the database providing little clue of what number corresponds to what expression and query type? When I had to do specific analysis through back end for PS-Queries, I found it difficult to decode these numeral values. After spending some time with different type of expression join criterion this is what I found, the below list displays the number values stored in EXPRTYPE field in PSQRYCRITERIA record along with its description of what it stands for?

• 0 - effective sequence
• 1- constant
• 2 – field
• 3 – expression
• 4 – subquery
• 5 – list
• 6 - current date
• 7 – tree
• 8 – prompt
• 9 - const-const
• 10 - const-field
• 11 - const-expr
• 12 - field-const
• 13 - field-field
• 14 - field-expr
• 15 - expr-const
• 16 - expr-field
• 17 – expr-expr