When we run the show command, e.g. show table db.tablename; show view db.viewname, it lists the object definition. I believe it will query the dictionary tables and rebuild .
Could you help us to understand how it queries the internal tables?
1 Answer
For a SHOW TABLE the parser actually creates the CREATE TABLE based on the current definition.
But for SHOW VIEW, etc. it's retrieving the CREATE from dbc.TablesV.RequestText. If the source code is larger than 12.5 KB RequestTxtOverFlow is set and the remainder is found in one or more 32 KB chunks in dbc.TextTbl.
For SHOW PROCEDURE it's different, this returns the internally stored sorce code (unless the SP is created with the NOSPL option), there's no way to access this info using a Select.
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Thanks for the answer. For Requesttext column in dbc.tablesv for views and dbc.tvm for tables returns the text of the most recent data definition statement If you perform alter on view or table at that time requesttext column returns alter statement.show command still shows the DDL instead of alter. It will considers the data of requesttext column and does some internal operations / manipulations on dictionary tables and gets the data. Not sure how exactly it works. Commented Jun 11, 2018 at 4:32
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As I wrote: for Tables the parser creates the DDL (this info is returned by the Resolver accessing the metadata stored in the Table Header on each AMP), but for views, etc. it's in RequestText.– dnoethCommented Jun 11, 2018 at 5:57
SHOWorDESCRIBEthat rebulids anything. I think that PostgreSQL's client has an option that lets you do something like this. Please give the (exact) command you are running and the result yiu hope to obtain.