DBeaver is a universal database manager and SQL Client. It supports MySQL, PostgreSQL, Oracle, DB2, MSSQL, Sybase, Mimer, HSQLDB, SQLite, Derby, and any database that has a JDBC driver. It is a GUI program that allows you to view the structure of a database, execute SQL queries and scripts, browse and export table data, handle BLOB/CLOB values, modify database meta objects, etc. It has a native UI (provided by the Eclipse SWT library), great performance, and relatively low memory consumption.
SQLet allows you to directly execute SQL on multiple text files, right from the Linux commandline. In one single command, you can read in text files (with or without header lines) and perform arbitrary select statements, including joins over several files. SQLet can thus replace awk or grep in some instances.