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POEnforce/check uniqueness of primary key across multiple tables
 

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    <p>I'm doing a data format conversion from Program A's CSV format to Program B's CSV format.</p> <p>Program A's format looks like:</p> <pre><code>Fruit, Orange, $1.99 Fruit, Apple, $2.99 Fruit, Pear, $5.99 Colour, Red, #FF0000 Colour, Green, #00FF00 Colour, Blue, #0000FF Colour, Orange, #FF8800 </code></pre> <p>I've converted Program A's CSV file into an SQLite database containing multiple tables, one for each type of record in the original CSV file. Here that would be <code>Fruit</code> and <code>Colour</code>. This maps well onto Program B's file format, which uses similar tables (with a few funky conversions required.)</p> <p>Each table in Program A's CSV file has an ID primary key which is not required to be unique. That is, there can be a "<code>Fruit</code>" row with ID "<code>Orange</code>" and also a "<code>Colour</code>" row with ID "<code>Orange</code>".</p> <p><em>However Program B would consider this an error</em> - it requires the ID primary key to be unique across ALL tables.</p> <p>What is an efficient way to detect non-unique ID keys, either in the original file (formatted like above) or in the SQL database? There are dozens of tables and thousands of records.</p> <p>My current approach is similar to (Python code):</p> <pre><code>import sqlite3, collections db_conn = sqlite3.connect('db.sqlite3') db_conn.row_factory = sqlite3.Row IDs = [] # build a list of (ID, table_name) pairs tables = ['Fruit','Colour']; for table in tables: rows = db_conn.execute("SELECT ID FROM %s" % table) for row in rows: IDs.append( (row['ID'],table) ) id_counts = collections.Counter([x(0) for x in IDs]) duplicated_ids = [x for x in id_counts if id_counts[x] &gt; 1] for duplicated_id in duplicated_ids: duplicated_types = [x(1) for x in IDs if x(0) == duplicated_id ] print ("Duplicate ID %(duplicated_id)s used for %(duplicated_types)s" % locals()) </code></pre> <p>This seems hilariously inefficient. There must exist a more elegant/more Pythonic way of doing this, possibly using some kind of set notation.</p> <p>Alternately, could I define my SQL schema (SQLite flavoured) so that SQLite enforces uniqueness of the ID across all tables?</p>
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