PostgreSQL/From MySQL

The following table shows how to get around some of the weird MySQL-specific, non-standard SQL syntax.

Note

After a bunch of editing here, I found this "Converting MySQL to PostgreSQL" wikibook.

MySQL	PostgreSQL	Supported by both?
LIMIT offset, count	LIMIT count OFFSET offset	Yes
MATCH (column(s)) AGAINST query	ftsindex @@ query::tsquery	No(1)
IFNULL(expr1, expr2)	CASE WHEN expr1 IS NULL THEN expr2 ELSE expr1 END	Yes
REPLACE INTO table (pkcolumn, column2) VALUES ('key', 'value2')	INSERT INTO table (pkcolumn, column2) SELECT 'key', 'value2' FROM table WHERE 'key' NOT IN (SELECT pkcolumn FROM table) LIMIT 1	No
BOOLEAN INT INT(n) INTEGER(n) TINYINT TINYINT(n) TINYINTEGER TINYINTEGER(n) MEDIUMINT MEDIUMINT(n) MEDIUMINTEGER MEDIUMINTEGER(n) SMALLINT SMALLINT(n) SMALLINTEGER SMALLINTEGER(n)	INTEGER	Yes(2)
BOOLEAN	INTEGER CHECK (column IN ('0', '1'))	No
INTEGER UNSIGNED	INTEGER CHECK (column > -1)	No
INTEGER SIGNED	INTEGER	Yes
INTEGER AUTO_INCREMENT	SERIAL PRIMARY KEY	No(3)
VARCHAR(n) CHAR(n) LONGTEXT BLOB LONGBLOB	TEXT	Yes(4)
DATETIME DATETIME NOT NULL DEFAULT '0000-00-00 00:00:00'	TIMESTAMP TIMESTAMP NOT NULL DEFAULT NOW()	No
'0000-00-00 00:00:00'	NOW()	No
CHARACTER SET UTF8 COLLATE UTF8_BIN		No(5)
column SET('value1', 'value2')	column TEXT CHECK (column IN ('value1', 'value2'))	No(6)
<columndef> COMMENT comment	COMMENT ON COLUMN column IS 'comment'	No
[UNIQUE] KEY indexname (column1, column2)	CREATE [UNIQUE] INDEX indexname ON tablename (column1, column2)	Yes

Notes

1. PostgreSQL full text searching is done with tsearch2, now integrated into PostgreSQL 8.3 or in contrib for earlier versions.
2. PostgreSQL has INT2 (SMALLINT), INT4 (INTEGER) and INT8 (BIGINT), but use INTEGER unless you want ones > 2³¹ in which case use BIGINT.
3. The SERIAL type is an auto-incrementing INTEGER sequence (implicitly created at CREATE TABLE time), maintained externally from the table (akin to an index). Autoincrementing integers suck in distributed scenarios, consider a UUID or composite key instead.
4. PostgreSQL couldn't care less, and stores them all as varying text anyway. Insisting on a length won't make it faster or use less disk space.
5. Create your database with UTF8 encoding.
6. As of 8.3 one can now go
   CREATE TYPE type AS ENUM ('value1', 'value2')
   column type

Useful magic MySQL incantation:

mysqldump fez_svn_empty -v -n --compatible=ansi,postgresql --complete-insert=TRUE --extended-insert=FALSE --compact --default-character-set=UTF8 -r fez_svn_empty.sql

For now, remove all KEY and FULLTEXT KEY declarations from the above sql file

Importing rows from a MySQL dump that uses INTEGER AUTO_INCREMENT for primary keys into a new PostgreSQL database using SERIAL primary keys is problematic. Options include:

1. reset the PostgreSQL sequences to start from MAX(idcolumn) + 1.
   SELECT MAX(idcolumn) + 1 AS startvalue
   ALTER SEQUENCE sequence RESTART WITH startvalue
2. edit the dump to remove idcolumn values from the INSERT statements (highly tedious and probably not easily scriptable)

Script To Update Sequences

A quick dirty script to update sequences to start from above the maximum value of the id field. Adjust to requirements.

#!/usr/bin/python
import sys
import string
from pyPgSQL import PgSQL

def main(filename):
    try:
        conn = PgSQL.connect(database='dbname', user='username', host='localhost', password='password')
        cur = conn.cursor()
    except PgSQL.Error, msg:
        print "*** PostgreSQL Connection Error: %s" % msg
        return 1

    try:
        f = open(filename, "r")
    except:
        print "*** File not found: %s" % filename
        return 1

    for line in f:
        if (line.find("CREATE TABLE ") != -1):
            tablename = line.split()[2]
            seqname = ""
        elif (line.find(" SERIAL ") != -1):
            columnname = line.split()[0]
            seqname = "\"%s_%s_seq\"" % (tablename.strip('"'), columnname.strip('"'))

        if seqname != "":
            maxsql = "SELECT MAX(%s)+1 AS seqrestart FROM %s;" % (columnname, tablename)
            cur.execute(maxsql)
            res = cur.fetchall()
            seqrestart = res[0].seqrestart
            if seqrestart > 0:
                seqsql = "ALTER SEQUENCE %s RESTART WITH %s;" % (seqname, seqrestart)
                print seqsql
                cur.execute(seqsql)
            seqname = ""
    
    cur.close()
    conn.commit()
    del cur, conn
    return 0

if __name__ == "__main__":
    sys.exit(main("/path/to/your_schema.sql"))