SQL序列和自增標(biāo)識(shí)的主要區(qū)別在于作用范圍和控制靈活性。1. 序列是獨(dú)立對(duì)象，可在多個(gè)表中使用，提供更靈活的配置選項(xiàng)，如起始值、步長(zhǎng)、最大值及循環(huán)行為，并需手動(dòng)調(diào)用生成下一個(gè)值；2. 自增標(biāo)識(shí)綁定特定表的列，自動(dòng)在插入新行時(shí)生成數(shù)值，配置簡(jiǎn)單但控制有限。選擇序列適用于跨表共享計(jì)數(shù)器或需要精細(xì)控制的場(chǎng)景，而自增標(biāo)識(shí)適合僅需為每張表生成唯一ID的簡(jiǎn)單情況。

A SQL sequence and an auto-increment identity both generate numeric values, often used for primary keys. The main difference lies in their scope and control: a sequence is an independent object that can be used across multiple tables and offers more flexibility, while identity is tied to a specific table column with simpler but less flexible behavior.

What Is a SQL Sequence?

A sequence is a standalone database object that generates a sequence of numeric values based on defined parameters like start value, increment, and maximum value.

• It’s not tied to any particular table.
• You can define how the numbers behave—like starting at 100 or skipping even numbers.
• You manually call the next value using a function like NEXT VALUE FOR (in SQL Server) or nextval() (in PostgreSQL).

Example use case:
You want a shared counter across multiple tables, like generating invoice numbers used by different departments.

Some common settings:

• Start value
• Increment amount (can be negative for descending sequences)
• Minimum and maximum values
• Cycle option (whether it wraps around when reaching limits)

What Is an Auto-Increment Identity?

An identity column automatically generates a numeric value for each new row inserted into a table.

• It's attached to a single column in a table.
• Usually starts at 1 and increments by 1.
• Automatically managed—you don’t need to reference it explicitly when inserting data.

Example use case:
You have a users table and want each new user to get a unique ID without manual input.

Pros:

• Simple to set up
• Automatically used during inserts

Cons:

• Harder to share across tables
• Limited control over gaps or cycling

Key Differences Between Sequence and Identity

• Scope: A sequence is global, usable by any table or application logic. An identity is local to one table column.
• Control: Sequences offer more configuration options. Identities are simpler but less customizable.
• Usage: With sequences, you must explicitly request the next value. With identities, the value is automatically generated on insert.
• Gaps: Both can have gaps due to rollbacks or deletions, but sequences may make it easier to manage this behavior if needed.

In short, choose a sequence if you need more control or cross-table usage. Use identity if you just want a simple, automatic unique ID per table.

That’s basically it — they serve similar needs but in different ways depending on your use case.

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