Here are some of the main factors:
The size of the data table: The size of the data table involved in the query directly affects the execution time of the query. The larger the amount of data in a table, the more time queries typically take to process.
Indexes: Query performance is often much improved if there are indexes on the columns involved in the query criteria. Without a proper index, the database may need to do a full table scan, which is often much slower than an index scan.
Complexity of the query: The complexity of the query, including the number of joins used, subqueries, aggregate functions, and so on, can affect the execution time of the query. More complex queries require more processing time.
Hardware and storage: The hardware (e.g., CPU, memory, disk speed) and storage configuration (e.g., disk type, IO performance) of the database server can affect query performance.
Concurrent load: The number of concurrent queries on the database server can also affect the performance of a single query. High concurrent loads can lead to resource contention, which can affect query speed.
Optimization of database management systems (DBMS): Different database management systems (such as MySQL, PostgreSQL, Oracle, etc.) have different query optimizers that may optimize queries differently.
Query optimization: How a query is written can also affect its performance. For example, using exists instead of in, or avoiding functions in where clauses, can improve query performance.
Data distribution: The distribution and pattern of your data, such as data skew, can also affect query performance. For example, if some values are very common in the table and some are very rare, this can lead to uneven query performance.
Network latency: If the database server and client are not on the same machine, network latency can also be a factor that can affect query performance.
Caching: Database query results and other related data may be cached in memory, improving subsequent query performance. However, the efficiency of caching is also affected by factors such as cache size, caching strategy, etc.
In order to optimize query performance, it is often necessary to consider these factors and take appropriate measures, such as creating appropriate indexes, optimizing query statements, and adjusting database configurations.