diff --git a/packages/server/src/api/routes/tests/datasource.spec.ts b/packages/server/src/api/routes/tests/datasource.spec.ts
index 0066be2a64..d5c0a256a1 100644
--- a/packages/server/src/api/routes/tests/datasource.spec.ts
+++ b/packages/server/src/api/routes/tests/datasource.spec.ts
@@ -6,7 +6,19 @@ import sdk from "../../../sdk"
 
 import tk from "timekeeper"
 import { mocks } from "@budibase/backend-core/tests"
-import { QueryPreview, SourceName } from "@budibase/types"
+import {
+  Datasource,
+  FieldSchema,
+  FieldSubtype,
+  FieldType,
+  QueryPreview,
+  RelationshipType,
+  SourceName,
+  Table,
+  TableSchema,
+} from "@budibase/types"
+import { DatabaseName, getDatasource } from "../../../integrations/tests/utils"
+import { tableForDatasource } from "../../../tests/utilities/structures"
 
 tk.freeze(mocks.date.MOCK_DATE)
 
@@ -223,4 +235,152 @@ describe("/datasources", () => {
       })
     })
   })
+
+  describe.each([
+    [DatabaseName.POSTGRES, getDatasource(DatabaseName.POSTGRES)],
+    [DatabaseName.MYSQL, getDatasource(DatabaseName.MYSQL)],
+    [DatabaseName.SQL_SERVER, getDatasource(DatabaseName.SQL_SERVER)],
+    [DatabaseName.MARIADB, getDatasource(DatabaseName.MARIADB)],
+  ])("fetch schema (%s)", (_, dsProvider) => {
+    beforeAll(async () => {
+      datasource = await config.api.datasource.create(await dsProvider)
+    })
+
+    it("fetching schema will not drop tables or columns", async () => {
+      const datasourceId = datasource!._id!
+
+      const simpleTable = await config.api.table.save(
+        tableForDatasource(datasource, {
+          name: "simple",
+          schema: {
+            name: {
+              name: "name",
+              type: FieldType.STRING,
+            },
+          },
+        })
+      )
+
+      type SupportedSqlTypes =
+        | FieldType.STRING
+        | FieldType.BARCODEQR
+        | FieldType.LONGFORM
+        | FieldType.OPTIONS
+        | FieldType.DATETIME
+        | FieldType.NUMBER
+        | FieldType.BOOLEAN
+        | FieldType.FORMULA
+        | FieldType.BIGINT
+        | FieldType.BB_REFERENCE
+        | FieldType.LINK
+        | FieldType.ARRAY
+
+      const fullSchema: {
+        [type in SupportedSqlTypes]: FieldSchema & { type: type }
+      } = {
+        [FieldType.STRING]: {
+          name: "string",
+          type: FieldType.STRING,
+          constraints: {
+            presence: true,
+          },
+        },
+        [FieldType.LONGFORM]: {
+          name: "longform",
+          type: FieldType.LONGFORM,
+        },
+        [FieldType.OPTIONS]: {
+          name: "options",
+          type: FieldType.OPTIONS,
+          constraints: {
+            presence: { allowEmpty: false },
+          },
+        },
+        [FieldType.NUMBER]: {
+          name: "number",
+          type: FieldType.NUMBER,
+        },
+        [FieldType.BOOLEAN]: {
+          name: "boolean",
+          type: FieldType.BOOLEAN,
+        },
+        [FieldType.ARRAY]: {
+          name: "array",
+          type: FieldType.ARRAY,
+        },
+        [FieldType.DATETIME]: {
+          name: "datetime",
+          type: FieldType.DATETIME,
+          dateOnly: true,
+          timeOnly: false,
+        },
+        [FieldType.LINK]: {
+          name: "link",
+          type: FieldType.LINK,
+          tableId: simpleTable._id!,
+          relationshipType: RelationshipType.ONE_TO_MANY,
+          fieldName: "link",
+        },
+        [FieldType.FORMULA]: {
+          name: "formula",
+          type: FieldType.FORMULA,
+          formula: "any formula",
+        },
+        [FieldType.BARCODEQR]: {
+          name: "barcodeqr",
+          type: FieldType.BARCODEQR,
+        },
+        [FieldType.BIGINT]: {
+          name: "bigint",
+          type: FieldType.BIGINT,
+        },
+        [FieldType.BB_REFERENCE]: {
+          name: "bb_reference",
+          type: FieldType.BB_REFERENCE,
+          subtype: FieldSubtype.USERS,
+        },
+      }
+
+      await config.api.table.save(
+        tableForDatasource(datasource, {
+          name: "full",
+          schema: fullSchema,
+        })
+      )
+
+      const persisted = await config.api.datasource.get(datasourceId)
+      await config.api.datasource.fetchSchema(datasourceId)
+
+      const updated = await config.api.datasource.get(datasourceId)
+      const expected: Datasource = {
+        ...persisted,
+        entities:
+          persisted?.entities &&
+          Object.entries(persisted.entities).reduce<Record<string, Table>>(
+            (acc, [tableName, table]) => {
+              acc[tableName] = {
+                ...table,
+                primaryDisplay: expect.not.stringMatching(
+                  new RegExp(`^${table.primaryDisplay || ""}$`)
+                ),
+                schema: Object.entries(table.schema).reduce<TableSchema>(
+                  (acc, [fieldName, field]) => {
+                    acc[fieldName] = expect.objectContaining({
+                      ...field,
+                    })
+                    return acc
+                  },
+                  {}
+                ),
+              }
+              return acc
+            },
+            {}
+          ),
+
+        _rev: expect.any(String),
+      }
+      expect(updated).toEqual(expected)
+    })
+  })
 })
diff --git a/packages/server/src/api/routes/tests/table.spec.ts b/packages/server/src/api/routes/tests/table.spec.ts
index 77e05b8e07..ede1e7af94 100644
--- a/packages/server/src/api/routes/tests/table.spec.ts
+++ b/packages/server/src/api/routes/tests/table.spec.ts
@@ -34,7 +34,7 @@ describe.each([
   [DatabaseName.SQL_SERVER, getDatasource(DatabaseName.SQL_SERVER)],
   [DatabaseName.MARIADB, getDatasource(DatabaseName.MARIADB)],
 ])("/tables (%s)", (_, dsProvider) => {
-  let isInternal: boolean
+  const isInternal: boolean = !dsProvider
   let datasource: Datasource | undefined
   let config = setup.getConfig()
 
@@ -44,9 +44,6 @@ describe.each([
     await config.init()
     if (dsProvider) {
       datasource = await config.api.datasource.create(await dsProvider)
-      isInternal = false
-    } else {
-      isInternal = true
     }
   })
 
diff --git a/packages/server/src/integrations/utils/utils.ts b/packages/server/src/integrations/utils/utils.ts
index cc75f0444d..5a6073ccab 100644
--- a/packages/server/src/integrations/utils/utils.ts
+++ b/packages/server/src/integrations/utils/utils.ts
@@ -4,10 +4,11 @@ import {
   Datasource,
   FieldType,
   TableSourceType,
+  FieldSchema,
 } from "@budibase/types"
 import { DocumentType, SEPARATOR } from "../../db/utils"
 import { InvalidColumns, DEFAULT_BB_DATASOURCE_ID } from "../../constants"
-import { SWITCHABLE_TYPES, helpers } from "@budibase/shared-core"
+import { helpers, utils } from "@budibase/shared-core"
 import env from "../../environment"
 import { Knex } from "knex"
 
@@ -15,7 +16,28 @@ const DOUBLE_SEPARATOR = `${SEPARATOR}${SEPARATOR}`
 const ROW_ID_REGEX = /^\[.*]$/g
 const ENCODED_SPACE = encodeURIComponent(" ")
 
-const SQL_NUMBER_TYPE_MAP = {
+type PrimitiveTypes =
+  | FieldType.STRING
+  | FieldType.NUMBER
+  | FieldType.BOOLEAN
+  | FieldType.DATETIME
+  | FieldType.JSON
+  | FieldType.BIGINT
+  | FieldType.OPTIONS
+
+function isPrimitiveType(type: FieldType): type is PrimitiveTypes {
+  return [
+    FieldType.STRING,
+    FieldType.NUMBER,
+    FieldType.BOOLEAN,
+    FieldType.DATETIME,
+    FieldType.JSON,
+    FieldType.BIGINT,
+    FieldType.OPTIONS,
+  ].includes(type)
+}
+
+const SQL_NUMBER_TYPE_MAP: Record<string, PrimitiveTypes> = {
   integer: FieldType.NUMBER,
   int: FieldType.NUMBER,
   decimal: FieldType.NUMBER,
@@ -35,7 +57,7 @@ const SQL_NUMBER_TYPE_MAP = {
   smallmoney: FieldType.NUMBER,
 }
 
-const SQL_DATE_TYPE_MAP = {
+const SQL_DATE_TYPE_MAP: Record<string, PrimitiveTypes> = {
   timestamp: FieldType.DATETIME,
   time: FieldType.DATETIME,
   datetime: FieldType.DATETIME,
@@ -46,7 +68,7 @@ const SQL_DATE_TYPE_MAP = {
 const SQL_DATE_ONLY_TYPES = ["date"]
 const SQL_TIME_ONLY_TYPES = ["time"]
 
-const SQL_STRING_TYPE_MAP = {
+const SQL_STRING_TYPE_MAP: Record<string, PrimitiveTypes> = {
   varchar: FieldType.STRING,
   char: FieldType.STRING,
   nchar: FieldType.STRING,
@@ -58,22 +80,22 @@ const SQL_STRING_TYPE_MAP = {
   text: FieldType.STRING,
 }
 
-const SQL_BOOLEAN_TYPE_MAP = {
+const SQL_BOOLEAN_TYPE_MAP: Record<string, PrimitiveTypes> = {
   boolean: FieldType.BOOLEAN,
   bit: FieldType.BOOLEAN,
   tinyint: FieldType.BOOLEAN,
 }
 
-const SQL_OPTIONS_TYPE_MAP = {
+const SQL_OPTIONS_TYPE_MAP: Record<string, PrimitiveTypes> = {
   "user-defined": FieldType.OPTIONS,
 }
 
-const SQL_MISC_TYPE_MAP = {
+const SQL_MISC_TYPE_MAP: Record<string, PrimitiveTypes> = {
   json: FieldType.JSON,
   bigint: FieldType.BIGINT,
 }
 
-const SQL_TYPE_MAP = {
+const SQL_TYPE_MAP: Record<string, PrimitiveTypes> = {
   ...SQL_NUMBER_TYPE_MAP,
   ...SQL_DATE_TYPE_MAP,
   ...SQL_STRING_TYPE_MAP,
@@ -239,14 +261,14 @@ export function generateColumnDefinition(config: {
     constraints.inclusion = options
   }
 
-  const schema: any = {
+  const schema: FieldSchema = {
     type: foundType,
     externalType,
     autocolumn,
     name,
     constraints,
   }
-  if (foundType === FieldType.DATETIME) {
+  if (schema.type === FieldType.DATETIME) {
     schema.dateOnly = SQL_DATE_ONLY_TYPES.includes(lowerCaseType)
     schema.timeOnly = SQL_TIME_ONLY_TYPES.includes(lowerCaseType)
   }
@@ -274,49 +296,6 @@ export function isIsoDateString(str: string) {
   return d.toISOString() === trimmedValue
 }
 
-/**
- * This function will determine whether a column is a relationship and whether it
- * is currently valid. The reason for the validity check is that tables can be deleted
- * outside of Budibase control and if this is the case it will break Budibase relationships.
- * The tableIds is a list passed down from the main finalise tables function, which is
- * based on the tables that have just been fetched. This will only really be used on subsequent
- * fetches to the first one - if the user is periodically refreshing Budibase knowledge of tables.
- * @param column The column to check, to see if it is a valid relationship.
- * @param tableIds The IDs of the tables which currently exist.
- */
-function shouldCopyRelationship(
-  column: { type: FieldType.LINK; tableId?: string },
-  tableIds: string[]
-) {
-  return (
-    column.type === FieldType.LINK &&
-    column.tableId &&
-    tableIds.includes(column.tableId)
-  )
-}
-
-/**
- * Similar function to the shouldCopyRelationship function, but instead this looks for options and boolean
- * types. It is possible to switch a string -> options and a number -> boolean (and vice versus) need to make
- * sure that these get copied over when tables are fetched. Also checks whether they are still valid, if a
- * column has changed type in the external database then copying it over may not be possible.
- * @param column The column to check for options or boolean type.
- * @param fetchedColumn The fetched column to check for the type in the external database.
- */
-function shouldCopySpecialColumn(
-  column: { type: FieldType },
-  fetchedColumn: { type: FieldType } | undefined
-) {
-  const isFormula = column.type === FieldType.FORMULA
-  // column has been deleted, remove - formulas will never exist, always copy
-  if (!isFormula && column && !fetchedColumn) {
-    return false
-  }
-  const fetchedIsNumber =
-    !fetchedColumn || fetchedColumn.type === FieldType.NUMBER
-  return fetchedIsNumber && column.type === FieldType.BOOLEAN
-}
-
 /**
  * Looks for columns which need to be copied over into the new table definitions, like relationships,
  * options types and views.
@@ -338,6 +317,9 @@ function copyExistingPropsOver(
     if (entities[tableName]?.created) {
       table.created = entities[tableName]?.created
     }
+    if (entities[tableName]?.constrained) {
+      table.constrained = entities[tableName]?.constrained
+    }
 
     table.views = entities[tableName].views
 
@@ -346,45 +328,73 @@ function copyExistingPropsOver(
       if (!Object.prototype.hasOwnProperty.call(existingTableSchema, key)) {
         continue
       }
+
       const column = existingTableSchema[key]
 
       const existingColumnType = column?.type
       const updatedColumnType = table.schema[key]?.type
 
-      // If the db column type changed to a non-compatible one, we want to re-fetch it
-      if (
-        updatedColumnType !== existingColumnType &&
-        !SWITCHABLE_TYPES[updatedColumnType]?.includes(existingColumnType)
-      ) {
-        continue
+      const keepIfType = (...validTypes: PrimitiveTypes[]) => {
+        return (
+          isPrimitiveType(updatedColumnType) &&
+          table.schema[key] &&
+          validTypes.includes(updatedColumnType)
+        )
       }
 
-      if (
-        column.type === FieldType.LINK &&
-        !shouldCopyRelationship(column, tableIds)
-      ) {
-        continue
+      let shouldKeepSchema = false
+      switch (existingColumnType) {
+        case FieldType.FORMULA:
+        case FieldType.AUTO:
+        case FieldType.INTERNAL:
+          shouldKeepSchema = true
+          break
+
+        case FieldType.LINK:
+          shouldKeepSchema =
+            existingColumnType === FieldType.LINK &&
+            tableIds.includes(column.tableId)
+          break
+
+        case FieldType.STRING:
+        case FieldType.OPTIONS:
+        case FieldType.LONGFORM:
+        case FieldType.BARCODEQR:
+          shouldKeepSchema = keepIfType(FieldType.STRING)
+          break
+
+        case FieldType.NUMBER:
+        case FieldType.BOOLEAN:
+          shouldKeepSchema = keepIfType(FieldType.BOOLEAN, FieldType.NUMBER)
+          break
+
+        case FieldType.ARRAY:
+        case FieldType.ATTACHMENTS:
+        case FieldType.ATTACHMENT_SINGLE:
+        case FieldType.JSON:
+        case FieldType.BB_REFERENCE:
+          shouldKeepSchema = keepIfType(FieldType.JSON, FieldType.STRING)
+          break
+
+        case FieldType.DATETIME:
+          shouldKeepSchema = keepIfType(FieldType.DATETIME, FieldType.STRING)
+          break
+
+        case FieldType.BIGINT:
+          shouldKeepSchema = keepIfType(FieldType.BIGINT, FieldType.NUMBER)
+          break
+
+        default:
+          utils.unreachable(existingColumnType)
       }
 
-      const specialTypes = [
-        FieldType.OPTIONS,
-        FieldType.LONGFORM,
-        FieldType.ARRAY,
-        FieldType.FORMULA,
-        FieldType.BB_REFERENCE,
-      ]
-      if (
-        specialTypes.includes(column.type) &&
-        !shouldCopySpecialColumn(column, table.schema[key])
-      ) {
-        continue
-      }
-
-      table.schema[key] = {
-        ...existingTableSchema[key],
-        externalType:
-          existingTableSchema[key].externalType ||
-          table.schema[key].externalType,
+      if (shouldKeepSchema) {
+        table.schema[key] = {
+          ...existingTableSchema[key],
+          externalType:
+            existingTableSchema[key].externalType ||
+            table.schema[key]?.externalType,
+        }
       }
     }
   }
diff --git a/packages/server/src/sdk/app/tables/tests/validation.spec.ts b/packages/server/src/sdk/app/tables/tests/validation.spec.ts
index 66b4222005..6f8efbaed1 100644
--- a/packages/server/src/sdk/app/tables/tests/validation.spec.ts
+++ b/packages/server/src/sdk/app/tables/tests/validation.spec.ts
@@ -125,7 +125,7 @@ describe("validation and update of external table schemas", () => {
   }
 
   it("should correctly set utilised foreign keys to autocolumns", () => {
-    const response = populateExternalTableSchemas(cloneDeep(SCHEMA) as any)
+    const response = populateExternalTableSchemas(cloneDeep(SCHEMA))
     const foreignKey = getForeignKeyColumn(response)
     expect(foreignKey.autocolumn).toBe(true)
     expect(foreignKey.autoReason).toBe(AutoReason.FOREIGN_KEY)
@@ -133,7 +133,7 @@ describe("validation and update of external table schemas", () => {
   })
 
   it("should correctly unset foreign keys when no longer used", () => {
-    const setResponse = populateExternalTableSchemas(cloneDeep(SCHEMA) as any)
+    const setResponse = populateExternalTableSchemas(cloneDeep(SCHEMA))
     const beforeFk = getForeignKeyColumn(setResponse)
     delete setResponse.entities!.client.schema.project
     delete setResponse.entities!.project.schema.client
diff --git a/packages/server/src/sdk/app/tables/validation.ts b/packages/server/src/sdk/app/tables/validation.ts
index 1609bdfcda..d71a156fdb 100644
--- a/packages/server/src/sdk/app/tables/validation.ts
+++ b/packages/server/src/sdk/app/tables/validation.ts
@@ -44,7 +44,10 @@ function checkForeignKeysAreAutoColumns(datasource: Datasource) {
       if (shouldBeForeign && !column.autocolumn) {
         column.autocolumn = true
         column.autoReason = AutoReason.FOREIGN_KEY
-      } else if (column.autoReason === AutoReason.FOREIGN_KEY) {
+      } else if (
+        !shouldBeForeign &&
+        column.autoReason === AutoReason.FOREIGN_KEY
+      ) {
         delete column.autocolumn
         delete column.autoReason
       }
diff --git a/packages/server/src/tests/utilities/api/datasource.ts b/packages/server/src/tests/utilities/api/datasource.ts
index 6ac624f0db..bb4c74093c 100644
--- a/packages/server/src/tests/utilities/api/datasource.ts
+++ b/packages/server/src/tests/utilities/api/datasource.ts
@@ -5,6 +5,7 @@ import {
   UpdateDatasourceResponse,
   UpdateDatasourceRequest,
   QueryJson,
+  BuildSchemaFromSourceResponse,
 } from "@budibase/types"
 import { Expectations, TestAPI } from "./base"
 
@@ -69,4 +70,13 @@ export class DatasourceAPI extends TestAPI {
       expectations,
     })
   }
+
+  fetchSchema = async (id: string, expectations?: Expectations) => {
+    return await this._post<BuildSchemaFromSourceResponse>(
+      `/api/datasources/${id}/schema`,
+      {
+        expectations,
+      }
+    )
+  }
 }
diff --git a/packages/types/src/documents/app/datasource.ts b/packages/types/src/documents/app/datasource.ts
index 8976e1cae3..32f5bbb132 100644
--- a/packages/types/src/documents/app/datasource.ts
+++ b/packages/types/src/documents/app/datasource.ts
@@ -13,9 +13,7 @@ export interface Datasource extends Document {
   config?: Record<string, any>
   plus?: boolean
   isSQL?: boolean
-  entities?: {
-    [key: string]: Table
-  }
+  entities?: Record<string, Table>
 }
 
 export enum RestAuthType {
diff --git a/packages/types/src/documents/app/table/schema.ts b/packages/types/src/documents/app/table/schema.ts
index 86c34b6a5c..63a5876bc0 100644
--- a/packages/types/src/documents/app/table/schema.ts
+++ b/packages/types/src/documents/app/table/schema.ts
@@ -91,6 +91,7 @@ export interface DateFieldMetadata extends Omit<BaseFieldSchema, "subtype"> {
   type: FieldType.DATETIME
   ignoreTimezones?: boolean
   timeOnly?: boolean
+  dateOnly?: boolean
   subtype?: AutoFieldSubType.CREATED_AT | AutoFieldSubType.UPDATED_AT
 }