{"id":13244,"date":"2022-10-03T11:45:36","date_gmt":"2022-10-03T06:15:36","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-if-two-tables-data-are-independant-but-they-have-relationship-one-main-another-sub-what-is-the-best-way-to-link-them\/"},"modified":"2022-10-03T11:45:36","modified_gmt":"2022-10-03T06:15:36","slug":"solved-if-two-tables-data-are-independant-but-they-have-relationship-one-main-another-sub-what-is-the-best-way-to-link-them","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-if-two-tables-data-are-independant-but-they-have-relationship-one-main-another-sub-what-is-the-best-way-to-link-them\/","title":{"rendered":"[Solved] If two Table&#8217;s data are independant, but they have relationship (one Main, another Sub). What is the best way to link them?"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-68870268\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"68870268\" data-parentid=\"68819917\" data-score=\"0\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>Well you are on your with the last comment creating a Foreign Key. So we have a relationship between Customers and Contacts. However the outstanding question becomes what type is Customer:Contact relationship?<\/p>\n<ul>\n<li>One-to-One (1:1)   -&gt; Each Customer has one contact and a Contact is for one customer.<\/li>\n<li>One-to-Many (1:M)  -&gt; Each Customer has many contacts and a Contact is for one customer.<\/li>\n<li>Many-to-Many (M:M) -&gt; Each customer has Many Contacts and Each Contact is for many customers.<\/li>\n<\/ul>\n<p>From your description discard 1:1. For 1:M the you include the customer PK in the contact table. For the M:M you actually create another table that contains the PK from both Customer and Contact.  <br \/>\nAs for generating ids do not even try to get the <strong>last one<\/strong> and increment it (generally referred to as MAX+1). In a multiple user environment it is a virtual guarantee you will get a duplicate. Simply create a <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.postgresql.org\/docs\/12\/sql-createsequence.html\">sequence<\/a> or a <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.postgresqltutorial.com\/postgresql-identity-column\/\">generated identity<\/a> for each table and Postgres will handle it.  <\/p>\n<p>Tables for 1:M, Postgres v10 and above<\/p>\n<pre><code>create table customers( cust_id    integer generated always as identity  \n                      , address    text\n                      , tel        text\n                      , fax        text\n                      , pay_terms  text\n                      , constraint cust_pk primary key (cust_id)\n                      ) \n                      \n create table contacts( cont_id    integer generated always as identity \n                      , cust_id    interger \n                      , tel        text\n                      , email      text\n                      , constraint cont_pk primary key (cont_id)\n                      , constraint cont_2_cust_fk \n                                   foreign key (cust_id)\n                                   references customers(cust_id) \n                      );\n<\/code><\/pre>\n<p>Table definitions for M:M, Postgres v10 and above<\/p>\n<pre><code>create table customers( cust_id    integer generated always as identity  \n                      , address    text\n                      , tel        text\n                      , fax        text\n                      , pay_terms  text\n                      , constraint cust_pk primary key (cust_id)\n                      ) \n                      \ncreate table contacts( cont_id    integer generated always as identity \n                     , cust_id    interger \n                     , tel        text\n                     , email      text\n                     , constraint cont_pk primary key (cont_id)\n                     );\n                      \ncreate table customer_contacts( cust_id integer\n                              , cont_id integer\n                              , constraint cust_cont_pk \n                                           primary key (cust_id, cont_id)\n                              , constraint cust_cont_2_cust_fk \n                                           foreign key (cust_id)\n                                           references customers(cust_id)  \n                              , constraint cust_cont_2_cont_fk \n                                           foreign key (cont_id)\n                                           references contacts(cont_id)\n                              );\n<\/code><\/pre>\n<p>For Postgres versions prior to v10, replace <code>integer generated always as identity<\/code> by <code>serial<\/code>.<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">2<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved If two Table&#8217;s data are independant, but they have relationship (one Main, another Sub). What is the best way to link them? <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] Well you are on your with the last comment creating a Foreign Key. So we have a relationship between Customers and Contacts. However the outstanding question becomes what type is Customer:Contact relationship? One-to-One (1:1) -&gt; Each Customer has one contact and a Contact is for one customer. One-to-Many (1:M) -&gt; Each Customer has many &#8230; <a title=\"[Solved] If two Table&#8217;s data are independant, but they have relationship (one Main, another Sub). What is the best way to link them?\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-if-two-tables-data-are-independant-but-they-have-relationship-one-main-another-sub-what-is-the-best-way-to-link-them\/\" aria-label=\"More on [Solved] If two Table&#8217;s data are independant, but they have relationship (one Main, another Sub). What is the best way to link them?\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324,623],"class_list":["post-13244","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-postgresql"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] If two Table&#039;s data are independant, but they have relationship (one Main, another Sub). 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