List of Databases Available in Amazon RDS Free Tier

A list of which Amazon RDS database engines are eligible for the AWS Free Tier and which are not.

[Amazon Redshift] TEXT type is converted to VARCHAR(256)

Amazon Redshift converts TEXT columns to VARCHAR(256) — a gotcha when coming from MySQL or PostgreSQL.

A Design Blueprint for AWS Commitment Discounts in 2026 — Layering Strategy After Database Savings Plans

AWS cost optimization has one cardinal rule: shrink first, then commit. With Database Savings Plans (December 2025) at the center, this post lays out a three-layer stacking design (Compute SP for general compute, Reserved Instances for stable data tiers) through the lens of application order, provisioning math, and multi-account governance. The 2026 question is not how to chase the deepest discount, but how to design financial flexibility that never blocks modernization.

BigQuery Data Recovery Methods

Links to BigQuery's time travel docs and Google Cloud's backup / DR strategy for data recovery.

BigQuery query to specify timezone and search with WHERE clause

A BigQuery Standard SQL WHERE clause filtering a date range with an explicit timezone.

Reading Notes: 'Data Management in 30 Minutes' by Yuzutaso and Haseryo

Reading notes introducing data management via 'Data Management in 30 Minutes.'

Google Data Studio Blended Data Not Recommended for Production Environment

Avoid Data Studio blended data in production — prep tables/views on the source and let Data Studio just display.

Procedure to Install MySQL5.5 from Source Code on CentOS6.3

Installing MySQL 5.5 from source on CentOS 6.3 with cmake, from build to initial setup and startup troubleshooting.

[CORESERVER] Database Backup Method

A quick memo on backing up a database from the CORESERVER management screen to the home directory.

How to Install dbt CLI [macOS Edition]

Installing dbt CLI on macOS via Homebrew and checking the version.

MySQL Setup Procedure for Specific Version [Docker Edition]

How to run a specific MySQL version on Docker, including the GRANT tweaks Docker for Mac needs.

[DB] Free ER Diagram GUI Editor "ER Master"

ER Master, a free ER-diagram GUI editor that runs as an Eclipse plugin.

[Heroku] How to Configure heroku-postgresql:dev

How to install the heroku-postgresql:dev add-on and promote it as the primary DATABASE_URL.

Heroku PostgreSQL Version Check Method and Command: heroku pg:info

Use heroku pg:info to confirm the version of Heroku PostgreSQL your app is running.

[Rails] How to Redo db:migrate to Heroku's Default PostgreSQL

Three ways to force db:migrate to run again on Heroku when rake db:reset is not available.

[Java 1.4] How to Embed Lists in PreparedStatement IN Clauses

Helper snippets for embedding a list into a PreparedStatement IN clause in Java 1.4.

[Java 1.4] How to Embed Lists in PreparedStatement IN Clause

Placeholder helper snippets for embedding a list into a PreparedStatement IN clause in Java 1.4.

Language Code Specification Memo

Reference links for the ISO 639 language code spec, handy when naming a DB column.

[Mac] Installing MySQL with Homebrew

Installing MySQL via Homebrew on macOS, setting up auto-start, and logging in as root.

[Mac] Installing Redis with Homebrew

Installing Redis via Homebrew, setting up launchctl auto-start, and connecting with redis-cli.

[MacOS] How to Uninstall All Versions of PostgreSQL ~ Homebrew Edition

Using brew uninstall --force to remove every Homebrew-installed PostgreSQL version on macOS, plus cleaning up the data directory.

[MacOS] Steps to Install PostgreSQL with Homebrew

Installing PostgreSQL on macOS via Homebrew — initdb, launchd auto-start, PGDATA, and a non-superuser account.

How to Configure MongoDB Atlas for Development Environment

Setting up MongoDB Atlas for development: free-tier region choice and Network Access whitelist notes.

[MongoDB] Backup with mongodump and Restore with mongorestore

mongodump / mongorestore commands for backing up and restoring a whole DB or a single collection.

[MongoDB] How to rename/change database names

Rename a MongoDB database by copyDatabase to the new name, then dropDatabase the old one.

[MySQL] Startup Fails with default-character-set

Fixing a MySQL 5.5 startup failure by switching my.cnf to character-set-server=utf8.

[MySQL] File './mysql-bin.index' not found (Errcode: 13)

Fixing the MySQL Errcode: 13 error on mysql-bin.index by giving the mysql user ownership via chown.

Change MySQL character encoding to UTF8

Steps to switch MySQL 5.7's character encoding to UTF8 via my.cnf.

[MySQL] Check the size of database and tables

SQL to check MySQL database and table sizes, and how to wrap it as a stored procedure.

Resolve Japanese character corruption in MySQL CLI with SET character_set_results=utf8mb4;

Fixing Japanese mojibake in the MySQL CLI with SET character_set_results=utf8mb4;.

[MySQL] Execute Queries from Command Line and Output to CSV File

Piping mysql -e output through sed to save query results as a CSV file.

[MySQL] CMake Error: Internal CMake error, TryCompile configure of cmake failed

Fixing MySQL source build errors on CentOS 6.3 by installing gcc-c++ and bison.

[MySQL] User Deletion Should Be Done with DROP USER, Not DELETE Statement

Why user deletion in MySQL must use DROP USER, not a DELETE statement.

[MySQL] SQLSTATE[HY000]: General error: 1030 Got error 28 from storage engine

The MySQL 'Got error 28 from storage engine' error is caused by a full disk.

[MySQL] How to Solve ERROR 1045 (28000): Access denied for user

Granting the FILE privilege to fix MySQL's Access denied error on SELECT INTO OUTFILE.

[MySQL] How to configure my.cnf (Mac + Homebrew Edition)

How to configure my.cnf for MySQL installed with Homebrew on Mac.

MySQL Query to Check Data Size of DB and Tables

SQL queries to check MySQL DB and table sizes for Aurora storage cost estimation.

[MySQL] Query Log File Cannot Be Specified Error / [ERROR] Could not use /var/log/myquery.log for logging (error 13)

Resolving MySQL's 'Could not use ... for logging (error 13)' startup failure via my.cnf.

[MySQL] Getting stuck with reserved words - ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'xxx' at line 1

MySQL threw ERROR 1064 on a query because the column name primary is a reserved word.

[Oracle] DESCRIBE Command to Check Table Definition

Oracle DESCRIBE plus the equivalent table-definition commands for MySQL and PostgreSQL.

[Oracle] Roles of Wildcard Characters - Percent (%) and Underscore (_)

A memo on Oracle's LIKE wildcards: % for any run of characters and _ for a single one.

[Oracle] Displaying Table List

Listing user tables in Oracle, MySQL, and PostgreSQL, side by side.

[Oracle] How to Resolve ORA-12505, TNS:listener does not currently know of SID given in connect descriptor Error

Fixing the ORA-12505 TNS listener error by restarting the listener and Oracle instance.

[Oracle] Automatic Sequential Number Generation Method

Using Oracle sequence objects with NEXTVAL / CURRVAL for auto-numbering.

[PostgreSQL][8.0.4] Sequence Function Arguments are text Type, not regclass Type (ERROR: cannot cast type text to regclass)

Fixing the PostgreSQL 8.0.4 'cannot cast type text to regclass' error in nextval.

[PostgreSQL] The Convenient COALESCE Function That Returns the First Non-NULL Argument

Using PostgreSQL's COALESCE function to substitute a default value when a column or aggregate returns NULL.

[PostgreSQL] ERROR: Cannot insert a duplicate key into unique index

Quick note on PostgreSQL's duplicate-key error when INSERT hits a UNIQUE constraint.

[PostgreSQL] How to Output Tables to CSV

Two ways to export a PostgreSQL table to CSV: interactive psql commands and a one-liner `psql -c` invocation.

[PostgreSQL] Configuration for Connecting from Other PCs

Configuring `listen_addresses` and pg_hba.conf so PostgreSQL accepts connections from other hosts.

[PostgreSQL] ERROR: missing FROM-clause entry for table

Handling the missing FROM-clause error in PostgreSQL, and what changed with add_missing_from in 9.0.

[PostgreSQL] ERROR: must be owner of extension plpgsql

Resolving `must be owner of extension plpgsql` on pg_dump import by granting the role superuser privileges.

[PostgreSQL] Check table permissions when ERROR: permission denied for ~ error occurs

Fixing PostgreSQL's permission denied error by checking table privileges with `\z` and running GRANT.

[PostgreSQL] ERROR: language "plpgsql" does not exist

Fixing PostgreSQL's missing plpgsql language by loading it with the `createlang` command.

[PostgreSQL] postmaster.opts is Auto-generated, So Editing It is Pointless

Notes on why editing postmaster.opts is pointless — it's regenerated on restart, so the startup script needs to change.

[Rails] Correspondence Between ActiveRecord and DB Data Types

A quick reference for how ActiveRecord column types map to native PostgreSQL and MySQL types.

[Ruby on Rails] find with ActiveRecord::RecordNotFound

Avoiding ActiveRecord::RecordNotFound by preferring find_by_id, which returns nil, over find.

[Ruby on Rails] How to Apply Row Locking with ActiveRecord (Optimistic Lock, Pessimistic Lock)

Reference links for learning ActiveRecord's optimistic and pessimistic row locking.

[Ruby on Rails] How to Add Foreign Key Columns to Other Tables (add_column, references)

Adding foreign key columns in Rails migrations, for both new tables and existing ones.

[Ruby on Rails] How to use arel_table

Reference links for learning how to use Rails' arel_table.

[Ruby on Rails] How to Change Default Values of Database Columns

Change a column's default value in Rails with change_column_default in a migration.

[Ruby on Rails] How to Initialize and Reset Database ~ rake db:reset and rake db:migrate:reset

rake db:reset vs rake db:migrate:reset in Rails, and when to reach for each.

Register initial data from CSV files with rails db:seed

Manage rails db:seed initial data as per-model CSV files and run seeds per model.

[Ruby on Rails][SQLite3] SQLException: Cannot add a NOT NULL column with default value NULL

The cause of the SQLite3 NOT NULL column error in Rails migrations, and two ways to fix it.

Summary of Good Books on Data Analysis and Engineering

Recommended books on data analysis and engineering, grouped into data infrastructure, ad-tech, and marketing & statistics.

[Redis] Command to get all values of keys containing a specific string

A one-liner combining redis-cli KEYS and MGET via xargs to fetch all values for keys matching a prefix.

Redis Replication (Master-Slave) Environment Setup [docker-compose Edition]

Setting up and verifying a Redis master-slave replication environment with docker-compose.

[Ruby] Data Types Available in DataMapper

A quick reference for the primitive data types supported by Ruby's DataMapper ORM.

Data Transfer from Amazon S3 to BigQuery

Gotchas from moving data from Amazon S3 to BigQuery via the BigQuery Data Transfer Service.

Shopify Uses MySQL as Their Database

Shopify uses MySQL, but you can't connect externally — migration means CSV export or the API.

When Duplicate Records Appear in Results, Suspect LEFT JOIN / INNER JOIN

When SQL results include duplicate records, suspect the LEFT JOIN / INNER JOIN keys first.

[Security] Essential Sites to Read When Understanding SQL Injection Countermeasures

A personal reading list of articles for understanding SQL injection countermeasures.

[SQLite] Getting Current Time in Japan Standard Time (JST) with datetime

Getting the current time in JST with SQLite by passing 'localtime' to the datetime function.

[SQLite] Firefox Add-on 'SQLite Manager' is Convenient!

Recommending the Firefox add-on 'SQLite Manager' as a convenient GUI for SQLite.

[SQLite] SQLite Manager - Firefox Extension for Operating SQLite

Introducing the Firefox extension 'SQLite Manager' for operating SQLite via a GUI.

Stopping Surprise Overage Bills on Supabase — Setting Up Spend Cap to Hand Databases to Vibe Coders Safely

You want to hand a Supabase database to non-developers, but you do not want a surprise pay-as-you-go bill when they blow past quota. Does Supabase have a setting that does not charge for overages? The short answer: the Free plan and the Pro plan's Spend Cap can pin your cost to a flat rate. Here is how it works, what it does and does not protect, the add-on loopholes, read-only mode behavior, and a safe configuration.

[Error] Invalid row key specified: ~ , referred to in ~

Fixing Symfony 1.4 `Invalid row key specified` fixture errors tied to foreign key relations.

[Symfony1.4] How to Create Multiple Relations to Columns in the Same Table

Declaring multiple relations to the same User table from a Symfony 1.4 schema.yml.

[Symfony2] About DB Master/Slave Configuration

Master/Slave DB options for Symfony2 — Doctrine DBAL's MasterSlaveConnection and EntityManager switching.

Prototyping on Vercel + Next.js Without an External DB: Comparing 6 Embedded Databases

A technical guide to selecting in-process databases for rapid prototyping under Vercel's ephemeral filesystem constraints.

[WordPress] Couldn't Edit Category from Admin Panel, So Resolved by Updating Database

Working around a WordPress category permission error by updating wp_terms directly in MySQL.

[ZF] Subqueries in FROM / WHERE Clauses with Zend_Db_Select

Reference links for writing FROM / WHERE subqueries with Zend_Db_Select.