How to Best Store Key-Value Pairs in a Relational Database?

Storing key-value pairs in a relational database

When storing key-value pairs in a relational database, consider the following:

Method 1: Dedicated key-value table

<code class="language-sql">CREATE TABLE key_value_pairs (
    itemid           varchar(32) NOT NULL,
    itemkey         varchar(32) NOT NULL,
    itemvalue       varchar(32) NOT NULL,
    CONSTRAINT ct_primarykey PRIMARY KEY(itemid, itemkey)
);</code>

This scheme allows easy insertion and retrieval of key-value pairs, but queries become complex due to the need to combine multiple rows.

Method 2: A series of key value columns

<code class="language-sql">CREATE TABLE key_value_pairs (
    itemid            varchar(32) NOT NULL,
    itemkey1        varchar(32) NOT NULL,
    itemvalue1      varchar(32) NOT NULL,
    itemkey2        varchar(32) NOT NULL,
    itemvalue2      varchar(32) NOT NULL,
    ...等等...
);</code>

This approach simplifies queries but limits scalability since the number of columns must be predetermined.

Other considerations

Before choosing an approach, consider the disadvantages of storing key-value pairs in a relational database:

• Lack of referential integrity: The database cannot enforce consistency between keys and values.
• Performance limitations: Joining generic key-value columns may not be as efficient as using specialized tables.

Often it is advantageous to create a separate table for each field (e.g. color, size, fabric). This provides better referential integrity, higher performance, and greater flexibility.

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