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MergeAttributes() has a loop to merge multiple inheritance parents into a column column definition. The merged-so-far definition is stored in a ColumnDef node. If we have to merge columns from multiple inheritance parents (if the name matches), then we have to check whether various column properties (type, collation, etc.) match. The current code extracts the pg_attribute value of the currently-considered inheritance parent and compares it against the merged-so-far ColumnDef value. If the currently considered column doesn't match any previously inherited column, we make a new ColumnDef node from the pg_attribute information and add it to the column list. This patch rearranges this so that we create the ColumnDef node first in either case. Then the code that checks the column properties for compatibility compares ColumnDef against ColumnDef (instead of ColumnDef against pg_attribute). This makes the code more symmetric and easier to follow. Also, later in MergeAttributes(), there is a similar but separate loop that merges the new local column definition with the combination of the inheritance parents established in the first loop. That comparison is already ColumnDef-vs-ColumnDef. With this change, both of these can use similar-looking logic. (A future project might be to extract these two sets of code into a common routine that encodes all the knowledge of whether two column definitions are compatible. But this isn't currently straightforward because we want to give different error messages in the two cases.) Furthermore, by avoiding the use of Form_pg_attribute here, we make it easier to make changes in the pg_attribute layout without having to worry about the local needs of tablecmds.c. Because MergeAttributes() is hugely long, it's sometimes hard to know where in the function you are currently looking. To help with that, I also renamed some variables to make it clearer where you are currently looking. The first look is "prev" vs. "new", the second loop is "inh" vs. "new". Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> Discussion: https://www.postgresql.org/message-id/flat/52a125e4-ff9a-95f5-9f61-b87cf447e4da@eisentraut.org |
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. Copyright and license information can be found in the file COPYRIGHT. General documentation about this version of PostgreSQL can be found at: https://www.postgresql.org/docs/devel/ In particular, information about building PostgreSQL from the source code can be found at: https://www.postgresql.org/docs/devel/installation.html The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.