建设部继续教育网站,小程序开发教程下载,网站建设招投标,网站开发电脑内存要多少在 MySQL 8 的 C 源码中#xff0c;表的最大字段数量限制体现在 MAX_FIELDS 宏定义中。这个宏定义了表中可以拥有的最大字段数量。
代码中的体现
在 mysql_prepare_create_table 函数中#xff0c;有以下代码段检查表的字段数量是否超过最大限制#xff1a;
cpp
if (alt…在 MySQL 8 的 C 源码中表的最大字段数量限制体现在 MAX_FIELDS 宏定义中。这个宏定义了表中可以拥有的最大字段数量。
代码中的体现
在 mysql_prepare_create_table 函数中有以下代码段检查表的字段数量是否超过最大限制
cpp
if (alter_info-create_list.elements MAX_FIELDS) {my_error(ER_TOO_MANY_FIELDS, MYF(0));return true;
}
这里alter_info-create_list.elements 表示表中字段的数量MAX_FIELDS 是最大允许的字段数量。
MAX_FIELDS 的定义
MAX_FIELDS 的定义通常在 MySQL 的头文件中例如 include/mysql_com.h 或其他相关头文件。在 MySQL 8 中MAX_FIELDS 的值为 4096。
源码位置
在 MySQL 8 的源码中mysql_prepare_create_table 函数位于 sql/sql_table.cc 文件中。这个文件包含了与表创建和修改相关的许多函数。
总结 最大字段数量MySQL 8 中表的最大字段数量为 4096。 代码中的体现在 mysql_prepare_create_table 函数中通过 MAX_FIELDS 宏检查表的字段数量。 MySQL 中每行记录的最大长度限制为 65,535 字节。这个限制是由 MySQL 的内部实现决定的而不是由某个特定的源码文件或函数直接定义的。这个限制适用于所有存储引擎包括 InnoDB 和 MyISAM。
限制的体现
在 MySQL 8 的源码中这个限制通常在多个地方体现特别是在处理表的创建和数据插入时。以下是一些关键点 表创建时的验证 在 mysql_prepare_create_table 函数中虽然没有直接的代码检查每行记录的长度但这个限制会在表创建时通过存储引擎的接口进行验证。 存储引擎的限制 每个存储引擎都有自己的限制。例如InnoDB 存储引擎在处理表创建时会检查每行记录的长度是否超过最大限制。 数据插入时的验证 在插入数据时MySQL 会检查每行记录的长度是否超过 65,535 字节。如果超过会报错。
示例代码
以下是一个简化的示例展示如何在插入数据时检查每行记录的长度
cpp
if (reclength file-max_record_length()) {my_error(ER_TOO_BIG_ROWSIZE, MYF(0),static_castlong(file-max_record_length()));return true;
}
在这个代码片段中reclength 是计算的每行记录的长度file-max_record_length() 是存储引擎允许的最大记录长度。如果 reclength 超过 file-max_record_length()则报错。
具体实现
在 MySQL 源码中file-max_record_length() 通常由存储引擎的实现提供。例如在 InnoDB 存储引擎中这个值被定义为 65,535 字节。 C源码
// Prepares the table and key structures for table creation.
bool mysql_prepare_create_table(THD *thd, const char *error_schema_name, const char *error_table_name,HA_CREATE_INFO *create_info, Alter_info *alter_info, handler *file,bool is_partitioned, KEY **key_info_buffer, uint *key_count,FOREIGN_KEY **fk_key_info_buffer, uint *fk_key_count,FOREIGN_KEY *existing_fks, uint existing_fks_count,const dd::Table *existing_fks_table, uint fk_max_generated_name_number,int select_field_count, bool find_parent_keys) {DBUG_TRACE;/*Validation of table properties.*/LEX_STRING *connect_string create_info-connect_string;if (connect_string-length ! 0 connect_string-length CONNECT_STRING_MAXLEN (system_charset_info-cset-charpos(system_charset_info, connect_string-str,(connect_string-str connect_string-length),CONNECT_STRING_MAXLEN) connect_string-length)) {my_error(ER_WRONG_STRING_LENGTH, MYF(0), connect_string-str, CONNECTION,CONNECT_STRING_MAXLEN);return true;}LEX_STRING *compress create_info-compress;if (compress-length ! 0 compress-length TABLE_COMMENT_MAXLEN system_charset_info-cset-charpos(system_charset_info, compress-str, compress-str compress-length,TABLE_COMMENT_MAXLEN) compress-length) {my_error(ER_WRONG_STRING_LENGTH, MYF(0), compress-str, COMPRESSION,TABLE_COMMENT_MAXLEN);return true;}LEX_STRING *encrypt_type create_info-encrypt_type;if (encrypt_type-length ! 0 encrypt_type-length TABLE_COMMENT_MAXLEN system_charset_info-cset-charpos(system_charset_info, encrypt_type-str,encrypt_type-str encrypt_type-length,TABLE_COMMENT_MAXLEN) encrypt_type-length) {my_error(ER_WRONG_STRING_LENGTH, MYF(0), encrypt_type-str, ENCRYPTION,TABLE_COMMENT_MAXLEN);return true;}// Validate table comment stringstd::string invalid_sub_str;if (is_invalid_string({create_info-comment.str, create_info-comment.length},system_charset_info, invalid_sub_str)) {my_error(ER_COMMENT_CONTAINS_INVALID_STRING, MYF(0), table,(std::string(error_schema_name) . std::string(error_table_name)).c_str(),system_charset_info-csname, invalid_sub_str.c_str());return true;}if (validate_comment_length(thd, create_info-comment.str, create_info-comment.length,TABLE_COMMENT_MAXLEN, ER_TOO_LONG_TABLE_COMMENT, error_table_name)) {return true;}if (alter_info-create_list.elements MAX_FIELDS) {my_error(ER_TOO_MANY_FIELDS, MYF(0));return true;}/*Checks which previously were done during .FRM creation.TODO: Check if the old .FRM limitations still make sensewith the new DD.*//* Fix this when we have new .frm files; Current limit is 4G rows (QQ) */constexpr ulonglong u32max UINT_MAX32;if (create_info-max_rows UINT_MAX32) {// Values larger than uint32_max are capped to uint32_max.// Emit a warning about this.push_warning_printf(thd, Sql_condition::SL_WARNING, ER_VALUE_OUT_OF_RANGE,ER_THD(thd, ER_VALUE_OUT_OF_RANGE), max_rows,create_info-max_rows, 0ULL, u32max, u32max);create_info-max_rows UINT_MAX32;}if (create_info-min_rows UINT_MAX32) {// Values larger than uint32_max are capped to uint32_max.// Emit a warning about this.push_warning_printf(thd, Sql_condition::SL_WARNING, ER_VALUE_OUT_OF_RANGE,ER_THD(thd, ER_VALUE_OUT_OF_RANGE), min_rows,create_info-min_rows, 0ULL, u32max, u32max);create_info-min_rows UINT_MAX32;}if (create_info-row_type ROW_TYPE_DYNAMIC)create_info-table_options | HA_OPTION_PACK_RECORD;/*Prepare fields, which must be done before callingadd_functional_index_to_create_list(). The reason is thatprepare_create_field() sets several properties of all Create_fields, such ascharacter set. We need the character set in order to get the correctdisplay width for each Create_field, which is in turn needed to resolve thecorrect data type/length for each hidden generated column added byadd_functional_index_to_create_list().*/int select_field_pos alter_info-create_list.elements - select_field_count;create_info-null_bits 0;int field_no 0;Create_field *sql_field;List_iteratorCreate_field it(alter_info-create_list);for (; (sql_field it); field_no) {if (prepare_create_field(thd, error_schema_name, error_table_name,create_info, alter_info-create_list,select_field_pos, file, sql_field, field_no))return true;}// Go through all functional key parts. For each functional key part, resolve// the expression and add a hidden generated column to the create list.for (Key_spec *key : alter_info-key_list) {if (key-type KEYTYPE_FOREIGN) continue;for (size_t j 0; j key-columns.size(); j) {Key_part_spec *key_part_spec key-columns[j];// In the case of procedures, the Key_part_spec may both have an// expression and a field name assigned to it. But the hidden generated// will not exist in the create list, so we will have to add it.if (!key_part_spec-has_expression() ||(key_part_spec-get_field_name() ! nullptr column_exists_in_create_list(key_part_spec-get_field_name(),alter_info-create_list))) {continue;}Create_field *new_create_field add_functional_index_to_create_list(thd, key, alter_info, key_part_spec, j, create_info);if (new_create_field nullptr) {return true;}// Call prepare_create_field on the Create_field that was added by// add_functional_index_to_create_list().assert(is_field_for_functional_index(new_create_field));if (prepare_create_field(thd, error_schema_name, error_table_name,create_info, alter_info-create_list,select_field_pos, file, new_create_field,field_no)) {return true;}}}// Now that we have all the Create_fields available, calculate the offsets// for each column.calculate_field_offsets(alter_info-create_list);/*Auto increment and blob checks.*/int auto_increment 0;int blob_columns 0;it.rewind();while ((sql_field it)) {if (sql_field-auto_flags Field::NEXT_NUMBER) auto_increment;switch (sql_field-sql_type) {case MYSQL_TYPE_GEOMETRY:case MYSQL_TYPE_BLOB:case MYSQL_TYPE_MEDIUM_BLOB:case MYSQL_TYPE_TINY_BLOB:case MYSQL_TYPE_LONG_BLOB:case MYSQL_TYPE_JSON:blob_columns;break;default:if (sql_field-is_array) blob_columns;break;}}if (auto_increment 1) {my_error(ER_WRONG_AUTO_KEY, MYF(0));return true;}if (auto_increment (file-ha_table_flags() HA_NO_AUTO_INCREMENT)) {my_error(ER_TABLE_CANT_HANDLE_AUTO_INCREMENT, MYF(0));return true;}if (blob_columns (file-ha_table_flags() HA_NO_BLOBS)) {my_error(ER_TABLE_CANT_HANDLE_BLOB, MYF(0));return true;}/*CREATE TABLE[with auto_increment column] SELECT is unsafe as the rowsinserted in the created table depends on the order of the rows fetchedfrom the select tables. This order may differ on master and slave. Wetherefore mark it as unsafe.*/if (select_field_count 0 auto_increment)thd-lex-set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_CREATE_SELECT_AUTOINC);/*Count keys and key segments.Also mark redundant keys to be ignored.*/uint key_parts;Mem_root_arraybool redundant_keys(thd-mem_root,alter_info-key_list.size(), false);if (count_keys(alter_info-key_list, key_count, key_parts, fk_key_count,redundant_keys, file-ha_table_flags()))return true;if (*key_count file-max_keys()) {my_error(ER_TOO_MANY_KEYS, MYF(0), file-max_keys());return true;}/*Make KEY objects for the keys in the new table.*/KEY *key_info;(*key_info_buffer) key_info (KEY *)sql_calloc(sizeof(KEY) * (*key_count));KEY_PART_INFO *key_part_info (KEY_PART_INFO *)sql_calloc(sizeof(KEY_PART_INFO) * key_parts);if (!*key_info_buffer || !key_part_info) return true; // Out of memoryMem_root_arrayconst KEY * keys_to_check(thd-mem_root);if (keys_to_check.reserve(*key_count)) return true; // Out of memoryuint key_number 0;bool primary_key false;// First prepare non-foreign keys so that they are ready when// we prepare foreign keys.for (size_t i 0; i alter_info-key_list.size(); i) {if (redundant_keys[i]) continue; // Skip redundant keysconst Key_spec *key alter_info-key_list[i];if (key-type KEYTYPE_PRIMARY) {if (primary_key) {my_error(ER_MULTIPLE_PRI_KEY, MYF(0));return true;}primary_key true;}if (key-type ! KEYTYPE_FOREIGN) {if (prepare_key(thd, error_schema_name, error_table_name, create_info,alter_info-create_list, key, key_info_buffer, key_info,key_part_info, keys_to_check, key_number, file,auto_increment))return true;key_info;key_number;}}// If the table is created without PK, we must check if this has// been disabled and return error. Limit the effect of sql_require_primary_key// to only those SEs that can participate in replication.if (!primary_key !thd-is_dd_system_thread() !thd-is_initialize_system_thread() (file-ha_table_flags() (HA_BINLOG_ROW_CAPABLE | HA_BINLOG_STMT_CAPABLE)) ! 0 thd-variables.sql_require_primary_key) {my_error(ER_TABLE_WITHOUT_PK, MYF(0));return true;}/*At this point all KEY objects are for indexes are fully constructed.So we can check for duplicate indexes for keys for which it was requested.*/const KEY **dup_check_key;for (dup_check_key keys_to_check.begin();dup_check_key ! keys_to_check.end(); dup_check_key) {if (check_duplicate_key(thd, error_schema_name, error_table_name,*dup_check_key, *key_info_buffer, *key_count,alter_info))return true;}if (!primary_key check_promoted_index(file, *key_info_buffer, *key_count))return true;/*Any auto increment columns not found during prepare_key?*/if (auto_increment 0) {my_error(ER_WRONG_AUTO_KEY, MYF(0));return true;}/* Sort keys in optimized order */std::sort(*key_info_buffer, *key_info_buffer *key_count, sort_keys());/*Normal keys are done, now prepare foreign keys.We do this after sorting normal keys to get predictable behaviorwhen searching for parent keys for self-referencing foreign keys.*/bool se_supports_fks (create_info-db_type-flags HTON_SUPPORTS_FOREIGN_KEYS);assert(se_supports_fks || existing_fks_count 0);(*fk_key_count) existing_fks_count;FOREIGN_KEY *fk_key_info;(*fk_key_info_buffer) fk_key_info (FOREIGN_KEY *)sql_calloc(sizeof(FOREIGN_KEY) * (*fk_key_count));if (!fk_key_info) return true; // Out of memory// Copy pre-existing foreign keys.if (existing_fks_count 0)memcpy(*fk_key_info_buffer, existing_fks,existing_fks_count * sizeof(FOREIGN_KEY));uint fk_number existing_fks_count;fk_key_info existing_fks_count;/*Check if we are trying to add partitioning to the table with existingforeign keys and tables storage engine doesnt support foreign keysover partitioned tables.*/if (is_partitioned existing_fks_count 0 (!create_info-db_type-partition_flags ||create_info-db_type-partition_flags() HA_CANNOT_PARTITION_FK)) {my_error(ER_FOREIGN_KEY_ON_PARTITIONED, MYF(0));return true;}/*Check that definitions of existing foreign keys are not broken by thisALTER TABLE. Update FOREIGN_KEY::unique_constraint_name if necessary.*/for (FOREIGN_KEY *fk *fk_key_info_buffer;fk (*fk_key_info_buffer) existing_fks_count; fk) {if (prepare_preexisting_foreign_key(thd, create_info, alter_info, error_schema_name, error_table_name,*key_info_buffer, *key_count, existing_fks_table, fk))return true;}// Prepare new foreign keys.for (size_t i 0; i alter_info-key_list.size(); i) {if (redundant_keys[i]) continue; // Skip redundant keysKey_spec *key alter_info-key_list[i];if (key-type KEYTYPE_FOREIGN) {if (prepare_foreign_key(thd, create_info, alter_info, error_schema_name,error_table_name, is_partitioned,*key_info_buffer, *key_count, *fk_key_info_buffer,fk_number, se_supports_fks, find_parent_keys,down_castForeign_key_spec *(key),fk_max_generated_name_number, fk_key_info))return true;if (se_supports_fks) {fk_key_info;fk_number;}}}/*Check if STRICT SQL mode is active and server is not started with--explicit-defaults-for-timestamp. Below check was added to prevent implicitdefault 0 value of timestamp. When explicit-defaults-for-timestamp serveroption is removed, whole set of check can be removed.Note that this check must be after KEYs have been created as thiscan cause the NOT_NULL_FLAG to be set.*/if (thd-variables.sql_mode MODE_NO_ZERO_DATE !thd-variables.explicit_defaults_for_timestamp) {it.rewind();while ((sql_field it)) {if (!sql_field-constant_default !sql_field-gcol_info is_timestamp_type(sql_field-sql_type) (sql_field-flags NOT_NULL_FLAG) !(sql_field-auto_flags Field::DEFAULT_NOW)) {/*An error should be reported if:- there is no explicit DEFAULT clause (default column value);- this is a TIMESTAMP column;- the column is not NULL;- this is not the DEFAULT CURRENT_TIMESTAMP column.And from checks before while loop,- STRICT SQL mode is active;- server is not started with --explicit-defaults-for-timestampIn other words, an error should be reported if- STRICT SQL mode is active;- the column definition is equivalent tocolumn_name TIMESTAMP DEFAULT 0.*/my_error(ER_INVALID_DEFAULT, MYF(0), sql_field-field_name);return true;}}}/* If fixed row records, we need one bit to check for deleted rows */if (!(create_info-table_options HA_OPTION_PACK_RECORD))create_info-null_bits;const ulong data_offset (create_info-null_bits 7) / 8;size_t reclength data_offset;it.rewind();while ((sql_field it)) {const size_t length sql_field-pack_length();if (sql_field-offset data_offset length reclength)reclength sql_field-offset data_offset length;}if (reclength file-max_record_length()) {my_error(ER_TOO_BIG_ROWSIZE, MYF(0),static_castlong(file-max_record_length()));return true;}return false;
}
